Originally the verse form was made widely acceptable by poets including Geoffrey Chaucer at that interesting period of English language development. The one that sealed the southern business variation he used as the choice of the educated and the court itself. The Knight's Tale (part of Chaucer's Canterbury Tales) sampled below is written in couplets, iambic pentameter and end-rhymed. The closed rhyme allows us to consider this as a direct antecedent of the heroic couplet but it is freer in form.
The pillers did their business and cure,
After the battle and discomfiture.
And so befell, that in the tas they found,
Through girt with many a grievous bloody wound,
Two younge knightes ligging by and by
Both in one armes, wrought full richely:
Of whiche two, Arcita hight that one,
And he that other highte Palamon.
Not fully quick, nor fully dead they were,
But by their coat-armour, and by their gear,
The heralds knew them well in special,
As those that weren of the blood royal
Of Thebes, and of sistren two y-born.
Out of the tas the pillers have them torn,
And have them carried soft unto the tent
Of Theseus, and he full soon them sent
To Athens, for to dwellen in prison
Perpetually, he n'olde no ranson.
So far so good (and I missing out the joys of Shakespear, Donne, Keats and so much more) but really it is our association of the heroic couplet as the verse form default of Dryden and Pope and the 18th century love of form that drove and sealed the nail in its coffin. In spite of the fact that neither used the form like this themselves - for example, an extract of Alexander Pope's poem the Rape of the Lock is playful with its couplets and its characters..as in this cynical view of the lady dressing
The Tortoise here and Elephant unite,
Transformed to combs, the speckled, and the white.
Here files of pins extend their shining rows,
Puffs, Powders, Patches, Bibles, Billet-doux.
Now awful Beauty puts on all its arms;
The fair each moment rises in her charms,
Repairs her smiles, awakens ev'ry grace,
And calls forth all the wonders of her face;
Sees by degrees a purer blush arise,
And keener lightnings quicken in her eyes.
The busy Sylphs surround their darling care,
These set the head, and those divide the hair,
Some fold the sleeve, whilst others plait the gown:
And Betty's prais'd for labours not her own.
But the form fell foul. It became a poetic tic for classical translations and epics which as time moved further from the wit and economy of Dryden and Pope's political and court commentary to imitators telling another big story - all set to the de-dum de-dum de-dum de-dum de-dum of iambic pentameter.
Heroic couplets became tangled with the literally heroic and then after the onset of the 20th century and its wars got brushed up alongside Walter Scott, Rupert Brooke and anyone else who had the misfortune to turn their writing eye on gallantry (however cynically).
Interesting what can happen to a poetic form.