It's a game of cat and mouse. The service keeps banning IP ranges, the user keeps reconnecting to different servers and regions. The server can't know exactly who's who, just that a bunch of users are using mullvad, while the user just need to find one server on one IP range that works.

Seems like a good deal to me. I don't care if they know I use mullvad, I care they don't know I'm me, and that's not something mullvad will easily disclose.