In the consumer space it touches a number of fronts. When you have a game people want to mod, you end up with a dev/community line of interaction where someone

In the consumer space it touches a number of fronts. When you have a game people want to mod, you end up with a dev/community line of interaction where someone ends up with the most popular mod/tool/forum/etc. and suddenly gains the power to wield mobs of players who will be upset if "their" mod breaks. It can quickly become a politicized scenario - who really "owns" the game? Does the modmaker get money? If the modmakers were making money, can the dev claim benefit? And so on. Even if the terms and agreements say one thing, the court of public opinion will say something else. Association with random third parties is risky and can damage a brand. Basically, the more you make ongoing support and "community leadership" part of your business model, the more room there is for the community to interfere with business goals and push for self-governance. This leads most game devs down the path of controlling everything and dictating terms: their game, their codebase, their servers, their account system, their official tournaments, etc. They often do things that make for a worse experience overall in the process, but it lets them set their own targets. With smaller developers there's more of an issue of not having the resources to support a community properly, and often stepping into success with no preparation for adopting any kind of collaborative governance. In those cases the community just generally overwhelms the dev and does whatever they want, fragmenting the game and creating various secondary power struggles in the process. It's all fairly vicious stuff. When you have something popular, everyone will look for an angle of personal profit, and while in other media the rules around derivative work are mostly known and straightforward, there are many original ways to create derivatives of games that have had little legal testing. Open sourcing is just a way of leaning toward a derivatives-encouraged stance, but it only describes part of the whole work(assets and any "live data" also count).