Here's an example of the type of composer I'm talking about. Self-taught. Doesn't read music. Hasn't studied theory.
I don't understand how not knowing theory or being unable to read music could possibly be a plus in a teacher.
One of the main reasons I'd seek out a teacher would be for him/her to say, "look, I can hear what you're trying for in this spot and it's not working because..." Music, at least a lot of commercial music, is not an uncharted wilderness that nobody has ever explored; on the contrary, a lot of ideas "just work," and I like a teacher who can help me get there faster. Not a cookie-cutter, but "here are three or four ways you could improve this passage," and start from there.
"I'd Like More of That Please"
We all can come up with four bars, maybe eight or sixteen, that sound really good. But then what? What if you have four weeks to write and produce a finished score of 70 minutes? It's a lot faster and less painless if you have three or four ways of looking at those sixteen bars you already wrote and analysing them, so you can work out what, exactly, is unusual and / or appealing about them. Theory is very good at helping to do that, and at propagating,
extending that bit you already composed so it forms the basis for a lot more music.
I do like a lot of music written by self-taught composers -- we can all think of them. Nevertheless, when faced with a ferocious deadline and needing to produce a thick stack of full-score orchestral music, either you need to know how to get the notes down the way you want or surround yourself with a lot of orchestrators help get it all done.
Maybe some find it more admirable to be self-taught? That's one thing when it comes to novels, but another, I think, when it comes to the orchestra. If you have a meaty project and a deadline, typically there's just too much to figure out if you're starting from scratch.