I've been on both sides of this. I've written, and I've negotiated these deals and so on. The fact is that in academic writing, the publishers have a huge advantage because the academics need to publish. You have a very willing seller and a not-very-willing buyer. They'll buy it or not buy it, and they're going to take most of the money for it.
It's a market issue, and if you get into it in the copyright reform, to try to fix the market, you go down that rabbit hole very fast and get into a lot of trouble.