People are regularly saying that he played solid minutes last year, but I'm seeing that he didn't even average 10 minutes a game and those were basically defensive minutes. He had that 15 point outburst against OU but even including that he averaged under 2 points a game.
My random uneducated guess is that TJ might just want the team to be better offensively and it might be worth giving those minutes to guys who can score, even if there's a slight dip in defense. Slight dip meaning still probably top 15 nationally.
As far as why he's not getting minutes when we're up 30, I guess that's valid to wonder, but it's also garbage time so I just don't think it matters a ton either way. Also, since they're playing 3 games in 3 days after a sparse schedule up to now, he might also want to keep the newer guys in as much as he can to properly get them into the groove of playing his system before conference play starts. As has been said a ton already, we're a deep team, and if Watson was getting minutes we'd be wondering why someone like one of our new transfers wasn't.