Once you deposit, your deposit is locked. These funds, along with the 10% tax, and exchange fees pays for the 1%. There's also a LP section in the reservoir that provides BNB funding.

There is a minting ability, but it has been tested under various conditions. So far they have not had to mint new tokens. You can read more about it in the Lightpaper: https://www.docdroid.net/0i3RJTu/drip-lightpaper-pdf

As far as why it's worth anything, it's providing a similar service to Bank CDs: money making money.