It does not make any sense why Watson didn't see minutes in the Colorado game. Speculating why is also completely fine for us fans to do, and what else would we talk about after a 30 point victory? Many of us, including me, would've loved to have seen him get some tick.
With all of that said, there's definitely a legitimate reason why he's not playing. Watson is obviously better than our walkons and Fish, and he's earned a right to see minutes in blowouts. He's either banged up and can't go full contact yet, there's a disciplinary reason (not bad enough to get suspended though), or he's transferring at the semester.