On one hand, having it like this can lead to an avalanche effect, where, because it looks like this one's going to win there's no point in trying to fund something you actually want this round, as everything goes to the winner anyway. On the other hand, keeping funds from round to round would mean some just sit there for months (possibly years) and inch penny by penny to the desired goal.
I can see the benefits and drawbacks to both formats.
At least this way, we do have a bit more options when it comes to choosing and funding compared to the previous method.