I love Proton but the idea of subscribing and committing to renew annually is a turn off. There's probably be a huge market behind the psychology of this.
They should offer a lifetime option for the core service and monetize the add-ons and new features.
Paying for a service that you use on an ongoing basis and that is very important (like email) is probably the best possible choice, since it aligns what you're paying for and what the company is working on. In the model you suggest the core service will atrophy slowly because the money is in the add-ons. This is why I'm happy to pay annually for my Fastmail account.
That's exactly the reason why so many people prefer giving up their data, their privacy, their freedom.
Personally I'm happy to pay proton a few bucks a month to not have to give up those things.
I'm not criticizing those that do, just that given my financial situation the trade off is simply not worth it.