Why should some barely paid above minimal wage coffee shop manager do that work either?

There’s no magical distinction between a coffee shop manager and barista.

I’m not suggesting that a barista or even the manager have some sort of moral or legal obligation to kick some asshole out of a store. They don’t have to do it. There are options. But generally speaking we all experience uncomfortable situations and you just deal with them like an adult in the best way you know how.