ah, the confused old man yells at clouds syndrome.Because everything -- including/especially rock music -- went south starting in 1970. Does the term "bubblegum music" ring a bell with you?
Back in my day we had real music.. there just isn't any good music these days
Bubblegum started in the 60's and lasted a few years.. and is also not relevant since there has always been pandering music.
Zeppelin IV came out in '71
Some bands you may not have heard of that put out some decent rock from 1970 on:
Van Halen
U2
AC/DC
Black Sabbath
Queen
The Ramones
Rush
Guns N Roses
Nirvana
ZZ Top
You get the idea