Many U.K. poets seem to take it as read that lyrics aren't poems and poems aren't lyrics. They dig their heels in over this distinction.
Such an argument would appear ridiculous in Spain, where songwriters publish collections of poetry and set many poems to music. A simple search of major Spanish poets on YouTube offers up many gems (especially Lorca and Alberti, etc), but perhaps my favourite is this one:
Luis Garcia Montero's poem led to Quique Gonzalez's song. Here are both of them, feeding off each other, lyrics as poetry and poetry as lyrics.
I feel decent singer-songwriters are marginalised in the U.K., while mainstream lyrics do tend to be trite, factors which lead to a belief that the two genres are somehow separate. In fact, the tools of both trades are shared: for example, Lennon and McCartney knew and used their metrics well, as do many contemporary writers for major groups. The main problem is the colossal dumbing down of popular music in Britain, blinding so many poets to the terrific collaborative possibilites that exist.