There are two reasons for not adopting the heroic couplet. First is its structure, which boxes up the content, packaging it into sections that deny the phrase by phrase expressiveness of Virgil's orginal. Second is Dryden's translation of 1697, still immensely readable.
            
            
 What makes a plenteous harvest, when to turn
            
 The fruitful soil, and when to sow the corn ;
            
 The care of sheep, of oxen, and of kine,
            
 And how to raise on elms the teeming vine ;
            
 The birth and genius of the frugal Bee,
            
 I sing, Maecenas, and I sing to thee.
            
 Ye deities ! who fields and plains protect,
            
 Who rule the seasons, and the year direct,
            
 Bacchus and fostering Ceres, powers divine,
            
 Who gave us corn for mast, for water, wine
            
 Ye Fauns, propitious to the rural swains,
            
 Ye Nymphs, that haunt the mountains and the plains,
            
 Join in my work, and to my numbers bring
            
 Your needful succour ; for your gifts I sing.
            
 And thou, whose trident struck the teeming earth,
            
 And made a passage for the courser's birth ;
            
 And thou, for whom the Csean shore sustains
            
 The milky herds, that graze the flowery plains ;
            
 And thou, the shepherds' tutelary god,
            
 Leave, for a while, O Pan ! thy loved abode;
            
 And, if Arcadian fleeces be thy care,
            
 From fields and mountains to my song repair.
            
 Inventor, Pallas, of the fattening oil,
            
 Thou founder of the plough, and ploughman's toil ;
            
 And thou, whose hands the shrowd-like cypress rear,
            
 Come, all ye gods and goddesses, that wear
            
 The rural honours, and increase the year;
            
 You, who supply the ground with seeds of grain ; {5}
            
            
So early Augustan verse with its balance and rugged good sense.
 
        
     
It is perfectly possible, with a little ingenuity, to create rhyming couplets in a more contemporary, fluid style:
            
            
 What gladdens cornfields, and what star inclines
            
 us turn the earth, Maecenus? How may vines
            
 be trestled by the elm? Or flocks be cared
            
 for, oxen bred? What qualities prepared
            
 the bees for hives? And you, celestial lights
            
 that lead the seasons in their fruitful rites,
            
 with Lider and kind Ceres, you who meet
            
 to turn the acorn lands to thick-sown wheat,
            
 and mix with Archeloüs new-made wine.
            
 10. You Fauns the rustics bless with wayside shrine —
            
 so dance you Dryad girls and gods — 
your source
            
 I celebrate. And Neptune's gift of horse
            
 when his great trident struck the earth, the ways
            
 of one who loves the wood, whose cattle graze
            
 15. the width of Ceos thicket lands, great Pan
            
 who guards Maenales lands and flocks of man,
            
 Come, leave your own Lycaeus groves and bring
            
 Minerva of the olive gift. I sing
            
 of one who showed us how curved plough should be,
            
 20. Sylvanus, bearer of the cypress tree,
            
 of gods and goddesses who guard our fields
            
 and in the unsown woods make good our yields,
            
 that heavens so plentifully give us rain.
            
 And you, great Caesar, who in time must gain . . .
            
            
 The rhyme requirements and shorter line length make it difficult to match the content properly, however, and the odd reader who can still appreciate such verse today would probably want to stay with the more conventional phrasing of Dryden.
Blank verse is more than able to render the Georgics effectively, and was indeed been the preferred choice in translations from the classics until 'free verse' became the norm. Again the arguments turn on history. There is no point in undertaking a new translation if the result is not a significant improvement on what is already available. J.B. Greenough's 1900 version, so often featuring on university Latin sites, is excellent:
            
            
J. B. Greenough 1900
            
            
What makes the cornfield smile; beneath what star
            
 Maecenas, it is meet to turn the sod
            
 Or marry elm with vine; how tend the steer;
            
 What pains for cattle-keeping, or what proof
            
 Of patient trial serves for thrifty bees;—
            
 Such are my themes. O universal lights
            
 Most glorious! ye that lead the gliding year
            
 Along the sky, Liber and Ceres mild,
            
 If by your bounty holpen earth once changed
            
 Chaonian acorn for the plump wheat-ear,
            
 And mingled with the grape, your new-found gift,
            
 The draughts of Achelous; and ye Fauns
            
 To rustics ever kind, come foot it, Fauns
            
 And Dryad-maids together; your gifts I sing. {22}
            
 It is not difficult to write something similar, updating the diction:
            
 What gladdens cornfields, and beneath what star
            
 Maecenas, are we made to turn the earth?
            
 How may the vine be fastened to the elm,
            
 or cattle tended, and the ox be bred?
            
 What knowledge is possessed by thrifty bees? —
            
 such are my themes. Celestial lights that lead
            
 the seasons in their fruitful dance. How Bacchus
            
 and propitious Ceres brought Chaonian
            
 acorn lands to thick-sown fields of wheat,
            
 10. and formed of Acheloüs new-made wine.
            
 And Fauns, you gods of country folk-so dance
            
 you Dryad girls and gods-your gifts I praise.
            
 And Neptune giving horse when your great trident
            
 struck the earth, and you, the woodland one
            
 whose snowy cattle browse the Ceos thickets;
            
 Pan that guards the flocks, though much you love
            
 Maenales lands, come, leave your own Lycaeus
            
 groves. And come Minerva, you of olive
            
 gift, the youth who first revealed the curving plough,
            
 20. Sylvanus, bearer of the cypress tree,
            
 and you, great gods and goddesses who watch
            
 our fields, to nourish fruits we have not sown,
            
 have heavens so bountifully water crops. . .
            
            
But again words have to be left out to squeeze the content, already terse in Latin, into the shorter English pentameter.
            
            
R.C. Trevelyan 1944
            
            
What makes the cornfield glad, beneath what star,
            
 Maecenas, it is well to turn the soil,
            
 And wed the vine to the elm, how to tend oxen,
            
 For nurturing flocks and hers what care is needful,
            
 For keeping thrifty bees what knowledge, now
            
 Shall I essay to sing. O ye most glorious
            
 Lights of the universe, that lead along
            
 Through heaven the gliding years; and you, Liber
            
 And kindly Ceres, by whose bounty earth exchanged
            
 Chaonian acorns for the rich ear of corn,
            
 And blended with pure water from the stream
            
 And new-found grape; and you Fauns, present deities
            
 Of country folk (draw together, Fauns
            
 And Dryad maidens), it is your gifts to men I sing. {12}
            
            
R.C. Trevelyan, a distinguished translator, avoided such compression by rendering ten of Virgil's hexameters by twelve English pentameters. Strangely, the result was not a success. The verse lacks the phrasing, cadences and extra graces so vital to blank verse, and something like half the lines are limp or clogged with unnecessary obstructions.
References can now be found in a free pdf compilation of Ocaso Press's Latin pages.