memes

Because of things like the North Hollywood Shootout. People don't want a situation where the criminals have much better weapons than the police. It doesn't matter that that kind of a situation is incredibly rare. People are scared and want police to never be outgunned.

Of course, that results in a bad situation where the cops in say Fluffy Landing, Florida have an armoured personnel carrier and don't need one. And, they get to train SWAT tactics just in case, but they never need those skills. And eventually when you have a hammer, every problem looks like a nail, so they use their APC for a regular arrest just because they want to justify having it, and they want to use their cool new toy.

It does vaguely make sense to have a SWAT team, especially in a big city in the USA. A sovereign state is basically defined by having a monopoly on the use of force within its own borders. If the bad guys (ACAB, but you know what I mean) can outgun the cops, then it can lead to chaos.

Also, politicians need to be seen as tough on crime to get elected. If you increase police funding, you're safe. If you cut police funding and there's some kind of incident, you can easily lose your next election.

In the US, there's no effective civilian control over police. Sure, theoretically the cops answer to the mayor or something. But, police unions are extremely powerful, and so mostly the cops get to do whatever they want.