I have been thinking that if I had lived in Columbo's LA in the 1970s I would be very nervous about seeing a professional in the city. It must have been murder city for the 1970s!

Also imagine the changes needed to the phone book as professionals vanish to prison etc.

So sad, so true, lol. No, seriously, I think it's because the type of murders Columbo solves are not typically 'the guy who hits someone over the head with a bottle' type murders (quote from Prescription:Murder) but are rather 'elaborate, intellectual projects' (another).

Well, add the other crime shows that took place in Los Angeles (e.g. Dragnet, Rockford Files, Adam-12, Mannix,etc, etc)
and you may be right! In fact the only
one that didn't in that era was Kojak which takes place in New York, but the studio scenes were also filmed in Los Angeles.
I lived in Los Angeles at the time and I recall that there were "society murders" of the type
Columbo solves occassionally.