I think most coaches are too scared to play pressure on defense or fast on offense. First, it takes too much control away from the coach and college coaches love to have a ton of control of what happens on the court. Second, especially on defense, you give up a lot of "easy" baskets (or at least that's often the perception) if you press the entire game. Granted, many (most?) coaches probably don't really look into what happens per possession if you play fast (or slow for that matter), but most coaches do not like giving up lay-ups, even if you force 3 turnovers for everyone you give up. Third, if it fails, it fails miserably and you get fired.