You'd think they could come up with a few new screams on the cheap. I wonder if in some way, just at the edge of our consciousness, we find the familiarity of Wilhelm's scream comforting. Instead of hearing a raw and unexpected scary noise that makes us think about what's actually happening to the movie character, we can sit back and say "Oh yes, someone's falling into a bottomless pit, I know what that sounds like."
Or maybe it satisfies a vicious and predatory part of our psyche that get squelched deep down in the back of our mind because we are Civilized, but secretly when we hear the scream we are grimly triumphant to hear that -- ha! -- old Wilhelm has gotten what he deserves once again.
Interesting. The same thing has happened with some laugh tracks on TV, as I understand it.
More and more Hollywood reminds me of a crazy great-Aunt who has a ton of money but still saves and reuses butter tubs.