Well, it usually installs from source, but that's not really the point. It's a package manager, it is trivial to give it it's own home, (and thankfully they made that an easy thing to do), but to throw it in that /usr/local bucket by default? It seems like a decision that requires real justification and the reasons I have seen seem pretty weak.
I mean, in the end it seems like almost nobody cares, but it's always been a pet peeve of mine.
I get what you're saying, but /usr/local is where I install stuff. I'm happy with having the thing that does little more than untangle my dependencies before running `make` for me with sane defaults use it too.
I expect to find system-specific applications in /usr/local. I get the argument otherwise, and it has merit, but not enough to not do it, if you get me.
Can I ask what you use your package manager for? My experience on the Mac is that it's mostly used by developers that want to install a package and don't want to have to manually install the 30 other dependencies by hand. For that use case, installing the dependencies along side the module that you actually wanted seems like an eminently reasonable thing to do, and certainly in my case it's pretty much exactly what I want from a package manager on the Mac. I assume if it bugs you that you have a different use case from mine. I would be interested to hear what it is (have I been missing opportunities on my Mac all this time???)
Right, that's what it's for, it's also why a 3rd party package manager shouldn't use it.