At the risk of breaking with getbig tradition and actually answering a question in this section legitimately, I'm guessing the difference is that 'sport' as it is loosely defined involves a competition where some physical performance (not necessarily that of the athlete solely or at all) is the pass/fail or marker. Which is why motorsport gets the nod, since it's still a competitive achievement to be the first across the line. And shit like that.
No doubt, bodybuilders are athletes and train as hard/long as is consistent with maximal results, but the contest itself is judged on aesthetics, not a physical performance as such.
Pro wrestling is a weird one, the results are a fix, of course, but it's no small thing to get in the ring and actually do that shit, I think it was Ken Shamrock who said he got far more injuries training/competing in wrestling than MMA.