Anyone who talks about poetry having lack of market success without considering rap to be poetry is defining their terms to get their result. Failing that, they need to set out precisely how it fails to be poetry.

How does rap fail to be poetry? Please show your working.

The usual style of complaint is that their favoured style of poetry is not sufficiently popular. Compare any fan of an out-of-favour style of anything complaining that no-one is interested in real X any more, therefore society has descended into philistinism. This is only slightly a caricature.

I don't even like rap and this one's glaring.