Not that the music of the 70's and 80's is better than the 50's and 60's, just different. The solo gave the guitarist a chance to show off his prowess, to jam. Guitar solos aren't the only solo, either, drummers and bassists got their chance too. I do believe that at some point the solo became overbearing, and it was time to get back to the song, if you know what I mean. I dont like to sit through a long 4 minute solo, even when it is done live......I get all antsy for the song to move on.
There are certain songs that just wouldn't seem right without the long solos. Like Inna-Godda-Da-Vida or Green Grass and High Tides.
I have a huge appreciation for the artists laying down the music foundation from the 50's and 60's but I do not particularly like those decades in music. I happen to like the jammin' rock n' roll years that followed