Checking with proton themself, the main reason seems to be to further resistance in case another instance of a issue they had in initial funding, where paypal blocked all payments to them. A wallet was also heavily requested by business users, and proton is using randomization to reduce tracking detailed on their site. So long as they next work on environmental impact to balance out this stuff, proton is fine still. Here is the code for the wallet: github.com/ProtonWallet