I honestly can't understand why Epic Games refuses to open-source Unreal 1 and UT99. They insist on licensing individual developers, instead of opening up the source so community forks can thrive. Look at the id tech community, with all the Doom and Quake forks, and all the amazing projects that spawned off of them.

The topic of "middleware" often comes up, as an excuse for them not being able to open the source. Well, just remove any third-party libraries and middleware, even EA did it with their C&C open-source releases. The C&C release did not even compile, but that did not stop the community from porting to Linux and other platforms, as well as modernizing the source and creating replacement libraries.