popular music - when did affectations become status quo?

Here’s what baffles me. There used to be music such as “the hills are alive with the sound of music…”

Nowadays, the above would have been distorted as follows: the hills are ALAHV…" Here’s more samples of distortions:

LLAHK EVER-BODY (like everybody
DO AH LAHK (do I like
AGIN (again
DOIN’ GOIN’ HAVIN’ (doing going having

I’m curious as to what caused these ugly-sounding distortions & affectations to become so trendy & status-quo. Furthermore, if it’s actually true that people enjoy these affected accents so much, then why don’t people talk that way in everyday language? Am I making sense or not? Isn’t that rather inconsistent? I’d have thought the British accent would have become more popular instead of the pop accent.