If a service is ever compromised, you would have chosen to consolidate information that would lead you to be more greatly vulnerable than if you had spread over multiple services.

…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.