The game companies won't offer managed game servers, because it's a totally new, small-market line of business outside their core competency. They won't open-source the server and let users run it themselves, because myriad licensing/IP/legalese reasons. Even if they did open source it, the stack likely isn't designed to scale down to a few bucks a month on the public cloud -- most users interested in running their own server wouldn't be happy with the actual cost of doing so. The handful of folks willing to pay for it won't move the needle.
Implementation aside, I think it’s primarily a money thing—the studios don’t care about this because the numbers say they shouldn’t.
Online-matchmaking becoming more and more centralized really made this starting to go away... It has both good and bad sides. One is much larger player pool and automated matchmaking. Other side is losing communities and more custom servers with custom maps...
i dont need a source code, i need a binary and a config file, some decent error logging and some basic documentation with how to get it running/common issues/requirements
that's it