What can happen, and actually happen in a lot of software fields, is multiple companies investing in the tool. That's the case for the Linux kernel, for databases, for programming languages...
Many game companies even have their own in-house engine. Instead of investing in that (usually sub-par) engine, they could be investing in an open Source engine.
I don't understand why this doesn't happen in games. And don't tell me that they want to keep their own engine as a competitive advantage, because most in-house engines are shit.