As we are used to how exchanges operates and make profits from different routes operating their platform and how they charge for listing of coins, trades and so on.
Now am not sure of how some of our developers are making their own profits by creating non custodial wallet for the bitcoin community users to enjoy, as Bitcoin wallet are free to download and use.
Well let me just put it this way everything isn't literally about money sometimes when it comes to something transparent and decentralized like Bitcoin enthusiasm comes into a play. Basically non-custodial open source wallet developers do not earn a dime directly from their applications or softwares they produce and manage that is the reason why they rely on both community support and most of the time donations from other enthusiast to fund the projects.