His performance at the combines was mediocre at best. A 4.91s 40-yd dash doesn’t cut it for an NFL defensive end.
Michael Sam weighs something like 260 pounds, and there were 320+ pound offensive linemen turning in faster 40-yard times than him.
Personally, I think the guy has no interest in playing football (maybe that's why his performance at the NFL combines was so poor) ... and that at some point he decided that "coming out" before the NFL draft was the best way to advance his most lucrative career prospect: as a professional homosexual.