to accomplish what other schools accomplish. No excuse for not trying, of course, but BYU's uniqueness is a real thing that makes recruiting harder — that is, even if BYU was pushing hard for international players, they likely wouldn't be able to get as many good guys as other schools can.
Elite programs can ask a lot of sacrifice, and players will accept it. I assume that's why volleyball doesn't have as much of a problem.
But how volleyball got to be an elite program in the first place, I don't know. But my guess? California LDS kids.