"Why does Kagi Search require an email address? We require an email address to be able to verify the account really belongs to you in the following cases:
To handle the account recovery (in case you lose your password) In case you contact us via email with an account related questions (in particular requests to delete your account or change your subscription) To occasionally send product updates, which you can disable in your Kagi settings or unsubscribe directly from the email Note that you can use an anonymous email provider such as SimpleLogin with Kagi Search and it is up to you what email address you want to use.
Kagi does not need your personal information and the above requirements are just bare minimums needed in order to be able to operate a subscription product business."
It's similar to services like Bitwarden in that regard.
Mullvad can get away with not doing that because they have a single plan with a low price.