And serve as the local authority there for at least awhile.

It might follow something like this pattern, sans prior residents: https://en.m.wikipedia.org/wiki/East_India_Company

A place inhospitable to life? Yeah, this sounds a great plan to waste all their resources...

Well hang on, making human life multi-planetary is extremely valuable, if not essential for our future survival. And we can use technology to make Mars hospitable.

Yes, but Apple is very unlikely to achieve that, as not only it doesn't only take money, but all the money on the earth wouldn't be able to achieve that with current tech (or even next-decades tech...) We should instead concentrate on mitigating the ongoing collapse of our civilization, so that the next one might get a shot at that ! (And Apple is not likely to help here, on the opposite, they are too invested in kicking the can, which makes things worse.)

How would that benefit their bottom line?

By having a planet where only Apple products are available and the inhabitants are a part of their cargo cult, maybe? hah

Taxation, typically.

Mars colonization would fit well, just like their recent products shiny and beautiful and utterly useless