I think there’s a few forces at work here on more personal levels.

1. A lot cops are veterans which means their background is focused on the use of force to rapidly end situations, which also means a lot of encounters are escalated quickly rather than de-escalated or prolonged via non-resolving techniques (i.e., conversation rather than just cuffing the person). Especially in countries that participated in the so-called GWOT they’re background is counter-insurgency so they’re trained to approach every environment being one that could immediately turn into a firefight and approach all situations like that.
2. A lot of cops are armed. Something about how if you have a hammer everything’s a nail…
3. They’re often true believers. Capital does deserve to be protected. Property deserves to be protected. Men with long hair are lazy hippies, and minorities (whoever that is in the context) are dehumanized outsiders. Cops are often personally reactionary: politically conservative, actively religious people who simply believe in the existing order.
4. Some just don’t give a shit and want the perks. Cops get their metaphorical dick sucked on a daily basis by basically everybody in politics and public life. They get sweet perks. They’re literally immune in same jurisdictions. That’s got to feel good.
5. Some of them are just bastards, but in a different way from points 3 or 4. Think of the Pinkertons shooting strikers: some were covered as true believers or like the other perks, but some just specifically like killing. How many Kyle Rittenhouses’s have become cops just to seek violence?

But fundamentally, they’re bastards even because if they aren’t true believers, it’s their job to blindly enforce laws. They’re literally paid to dissociate from any personal moral compass they may claim to have and just be an impersonal jackboot for the state. The job description of a cop is to follow orders, no questions asked. That’ll make anybody act the bastard.