Yeah, most of the 4e splat books for instance are out of print, and unlikely to get reprinted. Actually probably the majority of the 4e books are OOP at this point. A few might get reprinted but probably not most of them.
Virtually all gaming books get their initial print run and that's it. Even from the big guys like WotC. About the only thing that's usually an exception to that rule is the D&D basic rulebooks for the current edition (whatever TSR or WotC determined those to be).