This is only “clear” if you are completely unqualified to make such assertions but do so anyway to fit some narrative.
It’s not hard to discover why some departments have APCs (which are used extremely rarely) and how much they actually spend on them (almost nothing, they’re free). By and large, Police budgets go almost entirely to personnel costs.
LAPD spends 94.4% on salaries. That remaining 6.6% covers everything including equipment, helicopters, cars, body cams, firearms, IT infrastructure, forensics labs, and supporting services. They spent more on servers, radios, and body and dash cams alone than they did on ground vehicles.
http://www.lapdpolicecom.lacity.org/112415/BUDGET.pdf
You’re correct that a lot doesn’t have anything to do with stopping crimes though, but since that is not their primary responsibility (nor should we want it to be), this is expected. They are not psychic, so they cannot really act on a crime until the crime happens. As you can see from this thread, doing anything proactively is not something that the public wants. Most prefer to be left alone until they have done something wrong.
Nearly all of that gear was distributed by the DOD after the war and it was already paid for. Nearly all of it is never used. When it is used, it is in fact used for public safety. It’s not like they use the SWAT team to get groceries.