To run useful software.

I think the question is "how is this better or different than Linux or Windows", which it aims to replace? What are its design choices? Does it introduce any new concepts? For an example, see https://fuchsia.dev/fuchsia-src/concepts

I'm not asking for another Linux, just basic hardware support and a set of programs that I don't have to learn entirely from scratch.

What's the point of rewriting the whole stack?

There's a difference between making a Unix-compatible/Unix-like (a la Redox, Minix, Linux, the BSDs, macOS, etc) and having POSIX-compatibility + interfaces (a la Haiku, Serenity, Windows + Cygwin or WSL, etc).

One is just reinventing the wheel, even if it means "having useful software"; the other is attempting something new while offering tools to make porting useful OSS simpler.

As far as I see, Windows has always been different for the sake of it; it is a prime example of reinventing the wheel. What makes it good is its market share means things are almost always guaranteed to run on it, otherwise it is terrible and always has been since MS-DOS. If it didn't have "useful software", what else would it have going for it?