...because why would you go to all the trouble to pay Mullvad (presumably to keep your sensitive information away from big tech) to then give it to google in the form of an e-mail should you reach out to Mullvad for support? Google would then suck up any and all data that comes via their gmail service.
It's because of the difference in credentials. One is a website positing as having both privacy and cryptocurrency investment advice services, and the other is a random Lemur