VPNs are not 100% anonymous. They are not meant to be. Instead, they are meant to provide some level of privacy to law-abiding adults.
Most people would be embarrassed if their co-workers and neighbors knew the intimate personal details of their lives. Things they like, things they buy, things they do, etc. So, most people should use a VPN to protect their privacy.
By definition, 'most people' don't want or expect 100% anonymity online. They just want a bit of privacy in their personal life and their relationships. That's it.
VPNs don't protect (and are not intended to protect) criminals who want 100% anonymity from governments while committing online crimes. This is an important distinction. 'Most people' are not criminals and do not have this unrealistic expectation from Mullvad and other VPN providers.