Chicago's transition from hip, complex music to
pop music superstars was largly the result of internal pressure from
Peter Cetera, one of the founding members. Around 1990, oddly enough, Cetera felt that the group had gotten
too soft, and left to pursue a
solo career, in which he made more
soft rock.
Go figure.
Robert Lamm, the remaining band leader, tried to
move back to harder stuff, but when their project was complete Chicago's own
publishing company refused to put out their album.
If you think Chicago's music sounds like a bunch of cliched 70's music, that's only because all that crap that was done in the 70s was by musicians trying to copy the style of music that Chicago put out in the late 1960s. In this way, they're a lot like Nirvana, minus 20 years.