> Only I know the threat models I care about for any particular account I have.

You are not neccesarily the person being negatively effective.

Email service providers are all about reputation so their stuff isn't marked as spam. When your account gets hacked and starts sending viagra ads, you are not the one who suffers the fall out.

There are lots of email providers out there with different policies. One of the reasons gmail is popular is because of these policies.