Progressive rock bands were blistered from the time of The Sex Pistols onwards for being 'dinosaurs'. The press said so, therefor, it was correct.
Sadly, most (if not all) bought into it. Look at the two Yes albums after 'Going For The One' <and insert most band names>. Queen changed their approach earlier. As did band X, Y, and Z. Many capitulated, got lazy, and put out what they thought the buying public wanted.
(Reminds me of the old cartoons, such as the various Warner Bros. offerings of Bugs Bunny, Daffy Duck...Tom and Jerry, Bullwinkle, et al. The writers wrote what
they thought was funny, what
they found enjoyable, and wrote them mostly to crack themselves up.)
In so many ways, that's why the music of the 70s was so fantastic and diverse. Bands wrote (of course) what they hoped would sell, but the slant was more of what
they and their peers would enjoy.
It changed in the 80s. Madison Avenue said it had to, so it did. Sadly, too many bands drastically changed their style and what they were known for, that they lost their niche.