I don't know how much of that was due to Falk being too old to play Columbo by the late 80s/early 90s, how much of that was due to the writers, how much of that was Falk or studio interference behind the scenes, or even how much was just the entire tone of TV had shifted by then. About the tie Falk brings back Columbo in 1989, Miami Vice, Hunter, and In The Heat Of The Night were taking on serious stories for cop shows (although, to be fair we still had Matlock and Murder She Wrote for the paint-by-number murder shows), not to mention Cops.