Why were bushes so 'bushy' back then? Because they didn't feel any pressure to shave them, and if anything the societal pressure probably was in the other direction ("Why would a 'real man' shave or trim their pubes??").
The smooth and/or trimmed look in porn didn't really come into play until the 80s. In 70s porn you'll see more pubes and a lot of mustaches. I started looking at porn in the 80s, so by then the 70s stuff (which was almost all on 8mm film, and if it was on VHS, was originally shot and distributed on film and then transferred) looked dated to me and I wasn't a fan. If I recall right, Colt was one of the names in hairy mustache porn. I was more of a Cadinot or YMAC guy. 'Brian's Boys" was the first porn vid I ever saw, and set the tone for what turns me on.
Personally I'm a fan of neatly trimmed pubes and smooth chests, neither of which describes me btw. Once again we find that opposites attract, and I'm glad there are younger guys with smooth bodies out there who like older guys with hairy ones. Both sides are happy.