They want to become a money transfer service. The whole Bitcoin by email thing, it's a play to make themselves the middleman of a Venmo type architecture
So any two proton users who have the wallet enabled, can send and receive money seamlessly using their custodial key management.....
Sorry, I understand why a company would want to capitalize on the crypto bubble if it was 2022, but I meant this more as an existential "whyyyyy" but didn't have the energy for that.
All crypto-currencies are overhyped, almost cult-like trash that do nothing but create problems and waste energy. The whole lot of them, no exceptions and they will all fade away eventually, when the fad moves on.