"honestly can't even guess what problems can be addressed with something like this" The problem is that OS package managers install things globally. This is a

"honestly can't even guess what problems can be addressed with something like this" The problem is that OS package managers install things globally. This is a nightmare when developing, because * it makes much more difficult to handle multiple versions * as a consequence, it makes difficult to keep libraries updated, because package authors try to be conservative in what libraries they include in an operating system targeted at non-developers (in particular, latest versions of libraries are always lagging behind upstream) * it makes it hard to be sure that what you build on one computer will be reproducible on another one * even in the case where you know which dependencies you need (and you don't forget something just because you had already installed it), there is no simple way to document how to install them in such a way that the next user will be able to install everything with a single command * it requires root access when it is clearly not needed