With a lot of stuff the WWE does or in general, simplest answer is
They used to not like doing roster purges after it got used as a weapon against Linda for her political campaigns but now its probably more out of habit and not wanting other companies to take advantage of any drawing power remaining for people not being used well.
Think with their DVD/film stuff, its mostly because they don't lose as much money as other areas or are just trying to stay relevant in the mainstream with these crossovers.