He has a job and is part of a band, it seems as though he originally signed on to be part of just one show, then starred on two, they most likely are having Arin pick up the slack on Steam Train to give Danny more time.
Also, it's getting increasingly difficult to watch Arin play Sunshine, I understand the phenomenon of not having as much time to think about things while recording, playing blind and having to talk/be funny the whole time, but when they're using a walkthrough and he still doesn't get it, it's just a bit hard to watch.