It's the same thing a lot of companies' subscriptions do where they give you something extra over time so that they can take it away if you ever decide to try testing out another service. Normally it is something small though, like something decorative or just something saying that you've been a member for a long time, so at least they're giving you something useful for them to take away later, or maybe that makes it worse, I dunno~
It's like post-marketing. You're already a user/customer, but companies still want to put psychological hooks in you.
Kind of reminds me of steam's insane discounts or epic giving away games. That's more geared toward bringing people in, maybe.
I'd like to believe some instances of this sort of thing can be out of genuine appreciation for supporters, but I might just be naive... It is straight out of the abuser's handbook.
Honestly it's just a cool perk for me I use proton and use all thier services the only one I don't use is thier wallet but never had a issue. Works for my uses would love contact sync but I gave up on that and just self host EteSync on my Pi5.