Well, two things:
1) Doom's programming code is easier to work with than any of the games you list. There is a large mod community that knows how to work with that code.
2) You're looking a gift horse in the mouth. As always, if you can do a better job, do so! Make a total conversion for Quake II, Half-Life, Deus Ex, Unreal Tournament, or any other game of your choice. The rest of us are just grateful for what's been created. I don't think you're aware of the herculean effort that went into GB Doom.