There are several issues with open sourcing anything. Ownership is the first one. Who owns the code. Take something recent done with an unreal engine. Who o

There are several issues with open sourcing anything. Ownership is the first one. Who owns the code. Take something recent done with an unreal engine. Who owns that code? Most opensource licenses are very clear on who owns it as they are using copyright and contract law to back it up. The bits the dev added clearly are the studios code. But what about unreal that is fairly clearly not theirs to decide on. Then plugins they buy, those companies may or may not want to open source their code as that is what they sell to stay in business. You could make a case 'what about that 25 year old game'. Well that is interesting too as you still have to get owner approval. Yet the owner may not even know they own it. As the legal bits were long ago forgotten in some lawyers bottom filling drawer. Or for that matter want to pay someone to fixup that legal mess. That is assuming they even still have the code. When a company goes into 'sell everything' mode. They are not always very careful to keep that sort of thing around. They care more about 'these 20 chairs can get me 50 bucks a piece, and there are 30 computers worth 200 each' not what is on them. Most of the old code dumps we have access too are from companies that did care or someone who pack ratted it away in their desk drawer at home, or someone was sloppy with their security. Then on top of that. Many times before 2000 there was no real source control. Some companies did it. But many did not bother. It was a folder on 'jims' computer that was the golden copy. Then there is the idea of heritage. You made a game. But you made 6 games since then, each one building on the previous one. Would giving out that code mess you up somehow today? There are also those who can do all of those things. They just do not want to. This is the thing they sell. They are not going to give it away, at all.