This is not a thing that is really happening though. It's just some people on some media getting snobby about music. There have always been people who are more snobby about language (because it is about language and people, not music) than others. It's snobbery because it implies that one way is better than another. As with poetry, there are the dry ass 'intellectual' snobs, and there is the 'street'.

Parallel harmony, serialism, music that isnt western art(ragas,maqim) even jazz got away with what were once considered “errors”. Same reason people arent singing like Shakespeare, language changes and popular art follows the rules of the target audience.

Which songwriters?

Songwriters don't write in perfect grammar for the same reason most people don't speak in perfect grammar. Dialects are a reflection of different societal "clans", so to speak. We speak in different ways that appeal to others in our own clan. Lyrics written in academically perfect English would appeal to the highbrow academic clan but alienate everyone else. That's not exactly how you top the charts.

don’t get me weong, i’m a word guy all the way and i love a well turned phrase. but songwriting is also about visceral and emotional impact, and sometimes just sonic impact- the sound of the lyrics can be as important as the words themselves. in those cases, good grammar is less important to me than putting across whatever larger point i’m trying to make with the song.

I blame that early 2000s track The Way I Are 🤣