There could be any number of reasons it hasn't happened. I personally believe that they simply have left that in the past so they could move forward into new things as the show evolves, which is totally fair. Other possibilities include not having an episode slot for it, not having a full idea for it, or just not wanting to complicate things.In the end, if they don't bring back Peewee (which is most likely), I totally understand why. Though seeing him again would be pretty nice.