First, 70% of BYU speaks a second language. Yeah, BYU is a pretty white school. But there are a lot of people there who are pretty comfortable with international folks.
Second, a U.S. person transferring to BYU has to adjust to a new culture. An international person transferring has to adjust to a new culture wherever they go. They are expecting things to be a bit weird for them, so I think it's easier for them to handle the "weirdness" of Mormon culture.
Third, U.S. students often don't want to touch the honor code. But an international student who may not have other chances and just wants to play at a U.S. school might be more willing to make that pact.
Fourth, we have LDS people all over the world who could be sending BYU recruiting leads. Why not maximize the incredible global network that BYU has?