So why do the cops need a tank?

[HereSince1628]

32. I think it's not worth getting hung up on such things, tank was a slang term

that came about because in communication codes of WWI, the armored fighting vehicles were referred to as 'water tanks' to hide their actual purpose.

I do understand how anything and everything weaponized gets an aura that requires people to spew technical jargon about military designation numbers, length weight, munitions and optional points for attachment of accessories.

I suppose it could be argued that it's got some specific designation that sees it as a light armored fighting vehicle/wheeled.

But the point of the OP is what possible rationale is there for so many of them owned by municipal police forces. There are very few circumstances where a coaxial mounted large caliber machine gun is needed. Even mounted with a noise weapon, there are few circumstances that qualify as rationally justifiable, short of having every city ready to film movies about repelling 'the thing from Venus'.