A lot of their endpoints are rented or hosted from ASes that are well known, e.g. M247 Ltd. If I wanted to vastly reduce annoying VPN traffic, I'd simply block these ASes as well. That's likely the cause of these.

There isn't a lot Mullvad can do about it. Not all providers of hosting are willing to tolerate VPN endpoints in the same way they don't like hosting tor exit nodes.