I think bigger prizes get the attention of more professional developers and it's more scary for the beginners. While there were only smaller prizes, professionals were probably working on other things, but now they'll squeeze in time to work on some project for the competition, because it's worth their time.

Good ideas go long way to win a competition like this, but it needs to be implemented equally well, where pros have an advantage.
It's probably as with other competitions. Bigger prizes attract more pros and less beginners. Beginners don't think they can win so why bother.

In this competition it's good that the community will decide on the winners, which means more exposure for every application. On competitions where a small number of people decides, only the top applications get exposure while the others stay buried at the bottom.

I wanted to write my app for a while now, and this was a good motivation to get me started.

I don't think I can win, and all I'm hopping to get is the experience, from writing the app, and the extended exposure. Probably this way my app can get a bigger user base then if I released it outside of the competition.