Why did the 70s have so many detective/cop shows?

I enjoyed most of those ... I didn't ever watch McCloud ... the rest are good ... you missed chips '77-'83

Baretta, Starsky and Hutch and The Rockford Files were my favorites.

The 50s was full of cop shows too, you just didn't hear of most of them past Dragnet. There was Highway Patrol, Racket Squad, Gang Busters, The Untouchables, etc., most of them didn't last past a couple seasons or so.

Some possible theories:
1. They were the urban version of Westerns--usually a private detective or a cop who worked a little "outside the law," like some of the old Western heroes.  Except that the rural environment of Westerns was not in style in the 1970s (many "rural" shows in the early 1970s, although still popular, were cancelled by the networks, which wanted to court urban viewers, who presumably were younger and more likely to spend more). McCloud still managed to fit a cowboy persona into his cop role, though.

2. The economy was  bad in the 1970s, so crime was a compelling subject for plotlines. TV wasn't ready to show criminals as heroes, but they could get away with showing quirky, unconventional detectives and cops who often annoyed their by-the-book superiors, yet always got the case solved in the end.
Sometimes the cop/private detective heroes were shady enough to be taken for criminals (Rockford seemed a little suspicious, and Baretta was downright scary). 

I don't know why, but I'm sure glad it did.
Most of the shows you named were terrific.

The only ones I didn't like were the ones where solving crimes was more of a hobby than an occupation for the wealthy playboy detectives.
I'm referring mostly to BANACEK and BURKE'S LAW, although there were probably others.

Seems like there are a lot of cop shows on today too. (Doctor shows and lawyer shows have also been a target throughout the decades).

I'm in the (apparent) minority here in not caring much for those Seventies cop and detective shows, especially anything Quinn Martin produced. The success of two late Sixties series, Mannix and Hawaii 5-0, surely had something to do with those kinds of shows taking off. Of the cop shows, Columbo works best for me. I saw the other NBC 90 minute cop show (sort of), McMillan & Wife, and found it okay. Even when I liked the star, whether it was William Conrad or Telly Savalas, I just couldn't get into their shows. When it comes to crime, especially urban crime, I find color distracting, as well as the more realistic style of those shows. For that kind of TV I prefer the black and white shows of the late Fifties through the mid-Sixties. I guess I'm kind of a Luddite about some things.

maybe the success of dirty harry? wasn't born yet though.

Why were there so many cop shows in the 70s? A couple of other posters pretty much nailed it.  One said it was due to the economy back then and therefore violent crime was running rampant in the large American cities. It started to reflect on television and so cop shows became very popular. Another poster mentioned movies like Dirty Harry (and the sequels), which would have also had an impact on television. Certainly Harry Callahan may have influenced "tough cop" shows like Starsky and Hutch.