Probably some kind of tax dodge.
Probably established by Sami Al Arian's group, which set up a lot of large mosques here in Florida, particularly at the universities, etc. We have a very big one on the edge of town in Gainesville, although I don't know how big their congregation is; I thought it would be mostly foreign students at the university, but the only people I've ever seen are folks who look as if they are probably Black Muslims (or, more correctly, black American converts to Islam, since I believe the Black Muslim movement, per se, maintains a separate organization).