I think because it's a relatively easy idea to come up with, and the implementation details aren't earth-shattering. A year ago I was fixed on making a similar business called MeteorBill and worked part-time on it for a couple months before scrapping it .. I'm happy I did now, as my market research was clearly incomplete, and my UI was startlingly similar to yours and OP's. No great loss, I learned Erlang/OTP and Mnesia via that project.