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.