I can sorta see the "unfinished" aspect of this post- But I think it's far from bad. I never really even thought of it as "unfinished," but now that you mentioned like that and hearing how other companies have had releases and then their policy with DLC.
My guess is that it might be a combination of factors that have been mentioned.... Get the game released before summer- kids getting out of school and the overall theme of the game being paintball..... So, they probably wanted to at least get the overall "engine" of the game out at the hard deadline.... And then adding these other pieces gives them some flexibility, but then also keeps the game fresh among fans- gives us something to look forward to periodically like Hyrule Warriors or MK8.
If they play things right, we could still be talking about this game next year at this time......