I mean "because they are done" is a fine answer but...
When you go to the submissions page, are submissions listed in the order they were submitted?
Are you going to see the first submissions, first?
I don't actually know if the ordering changes based on anything else, but that could be a reason. Get seen, get more people to play your game. (I'm also totally unfamiliar with how voting works)
Edit: Or, hell, just in the hopes of getting some playtesting?
I've commented on a couple of the submitted games here and some of it was about when a feature doesn't work for me.
Which I'm hoping might be helpful.