Because you don't have to accept credit cards or enforce licenses? It is the least resistant path from someone's bank account to your bank account. The custom

Because you don't have to accept credit cards or enforce licenses? It is the least resistant path from someone's bank account to your bank account. The customer doesn't even take their credit card out of their wallet. Multiply that by the chance that they will accept your app (high), and you have good expected returns. As much as I want to sell offline web apps to any platform, that store doesn't yet exist.