Having recently been reacquainted with some poetry, I was reminded of this thread, which asked a good question. I am sure the answer is more complex than I suggest here, but some initial thoughts.
First we ought to note the place of poetry in contemporary Pakistan: it is part of everyday life to a much greater degree than many countries in the West. Poetry forms parts of lyrics of so many well-known songs. Think of Coke Studio, the preeminent musical event in Pakistan. From the top of my head, the lyrics, in a variety of languages, of the following high priests of poetry have been drawn on over the years in the Studio: Amir Khusrau, Bulleh Shah, Shah Latif, Khwaja Ghulam Farid, Iqbal, Faiz and Ghalib. I am no expert on English music but it seems hard to imagine the poems of Shakespeare or Wordsworth or Keats being so liberally relied on in the production of English music intended for mass consumption.
Poetic couplets also appear frequently on Pakistani trucks. Take the following couplet (from Jamal Elias’s book, On Wings of Diesel):
tum to nigahen pher ke kushiyon men kho gae
hum ne udasiyon ko muqaddar bana liya
All of this is of course as true of Urdu poetry as poetry in regional tongues. Even with its aristocratic origins, frequent use of vocabulary that is not in common use, Urdu poetry is a valued element of popular culture.
Second, we may mention that Urdu poetry as a descendant of Persian poetry draws on a rich history, evoking long-standing themes and a stock of familiar images and thereby representing a continuation of an enduring tradition.
Thirdly, it is specifically the ghazal which has been regarded as the most venerated form of Urdu literature. Although addressing a multitude of issues, it is above all associated with love - earthly and divine. The ghazal is made up of a series of couplets, each couplet independent of one another, but stitched together in a poem by rhyme and metre conventions. We should also remember that the ghazal was historically first heard (at a musha’ira) and only appeared in print later. What results from all this?
As a couplet contains a whole thought, it is often an impactful vehicle to express concisely a profound feeling or thought. A couplet is also easier to remember and memorise and this I would think accounts in some part to the popularity of Urdu poetry. And as the ghazal is also produced to be heard the rhythmic and rhyming patterns are often quite pleasing to the ear.
I owe the fourth point to [MENTION=144682]Sirris[/MENTION]:
“The irony of the thing is that in our south Asian tradition "romantic love" is looked down upon while the literature is full of deep sentiments.”
I think the appeal of the love lyric is perhaps enhanced by its subversive quality: the determined dedication to the ideals of love in a society which, in large parts of South Asia at least, has historically been unkind to romantic love.
Fifthly, as [MENTION=56933]ElRaja[/MENTION] has rightly stated, on a more functional level, Urdu seems well suited to the type of poetry described above, possessing more rhyming words than English, for instance.