Because in its current form the subject and verb don't agree.

I have no idea if what you're saying is generally true, but I can say with certainty that no one would ever say "the police is corrupt" in American English.

A better example might be a British soccer club, e.g. Chelsea are corrupt.

The police force are corrupt vs the police force is corrupt.

That second example is not valid in any English.

It could be valid if the subject is a British, new wave band, but otherwise, I agree with you.

Good try but an errant example. American English treats "police" as a plural noun (although maybe not always in Baltimore).

In the British style, "Microsoft have released a press briefing"; in American, "Microsoft has released a press briefing."