Everyone gets to submit at least one theme, but when somebody's theme gets voted on their ranking goes up and it goes down when a theme gets rejected. The top 10 submitters get into a special list where people can see all their submitted themes and they can submit (11 - Ranking) themes each. As people move in and out of the list and change ranking within it, the number of submissions they can make can only go up, to the maximum of 10. So in theory we get more of the best themes and fewer people have to sift through hundreds of garbage themes.