Its been awhile since I've seen it but Spinal Tap was making fun of a lot of bands like that, its part of their fictional band's backstory. They start out much like the Stones with some simple catchy early 60's tunes, turn into a hippie band, then quickly transform into metal in order to follow the money.
It's happened many times. Fleetwood Mac went from hard blues in the 1970s to straight pop in the 1980s. A surprising number of 1970s prog rock bands (Genesis, Yes, Rush, The Moody Blues) turned into 1980s synth pop bands.
Fleetwood Mac is a good example, actually. Regarding 1970s prog rock bands, their 80s work is for the most part still pretty original and musically honest. One notable outlier is Phil Collins whose solo stuff is truely aweful IMO. (How can you go from being the drummer of Genesis to writing "A Groovy Kind of Love"?)