Cobra, engines like Unreal and Unity will take a cut of a games sales once it passes some threshold. Crytek seems to be relying on the generosity of its users because from what I can tell there is no clause like that for CryEngine.
And yeah D, thats the trouble fro Crytek. No one is making use of their engine. Part of the problem they are having, and other engines have the same problem, is that Unreal and Unity have a major positive feedback loop working for them. The engines are well documented, which made more people use them, which helped keep the documentation up to date. Now that so many developers have experience working in either of those engines why would they switch to something else that that'd have to waste time getting the hang of?
