Because NXT is never about the actual wrestlers, or at least it hasn't been since Season 1. It is about Michael Cole putting himself over. Mason Ryan might not get buried, I'll give you that, altough with Michael Cole on NXT and him just ranting on and on and on about how bad the show is, it would hamper a little Ryan on itself.
But Seth Rollins is vowed to get ripped apart by Cole if placed on NXT. First off, he's indy, so WWE for him to get over will have Rollins bash him week in and week out, if yeah, that thing worked for Danielson...not so much for Kaval, so the third time around the effect will be even less imo. Besides, Rollins's promos, while good, are not something to be amazed with, and his voice is something Cole might pick apart
Yeah, I am grasping at straws, but it's NXT. They have had Cole pick apart almost every wrestler for the most idiotic of things. I think for example that Lucky Cannon got his career derailed by Michael Cole's commentary.