Copper won’t be chewed by rodents that unexpectedly gain access to the attic or crawl space, and it doesn’t degrade in sunlight.

Mini splits are sized for single rooms and the expected expansion path is to add more of them. That’s not too expensive if you are a handy DIYer who can deal with electrical and mechanical, but it’s not great if you’re paying installation labor. Similar story with everything else in the home improvement space.