Having one party in control of most major cities, where most crime is, for 50+ years now is working wonders.

One thing that puzzles me a bit about the U.S. is nonexistence of viable local parties. Something similar to the Scottish National Party in the UK or Freie Wähler in Bavaria.

How come that the entire political scene on all levels collapses into just two poles, with the predictable result that many places are de facto one party places?

Why doesn't America have local Ross Perots in various corners of the country, starting their own political parties specific for one place only?

We do. The Socialist Alternative are a viable party in places like Seattle, local politicians often run as independents aligned with organizations like DSA, etc.

And yet that party is still preferable to the alternative, according to the voters. Funny how that goes.

One of the really bad things about two party systems is that people start to consider their voting record a part of their personal identity. That leads to massive ossification of voting patterns in individuals.

In a multiparty system, it is much more normal to be a swing voter.