The useful part of a publisher is developmental editing (product) and copy editing (Q/A), so there is an opportunity for "lightweight" publishing companies that help expert authors produce the book—like self publishing, but you don't have to do the boring parts. I'm working in that space. We have two textbooks out: https://www.amazon.com/dp/0992001005/noBSmathphys and https://www.amazon.com/dp/0992001021/noBSLA
If you're a freshman in college, please check out my book: https://www.amazon.com/dp/0992001005/noBSguide It's super affordable and it will get you through MECHANICS and CALCULUS without too much suffering.
You won't get a degree or anything, but the knowledge will last with you longer than the case of beer ;)