I can imagine that the sites want to validate that you still have access to the email associated with the account, and asking people to check their settings is annoying, and they know no one will do it. I can also imagine that sites want to know as much about you as possible, don't want you to be using burner email addresses, and are probably selling the fact that your email address can still receive email to marketing firms who compile that info.

[–] Sprinks@lemmy.world 6 points 3 hours ago

Annual/routine email verification fills that need, though. For the sites i do support desk for, an email verification link is sent during account creation and then annually. If the email address is not verified then on login the account holder is prompted to either resend the verification link or change it and verify the new email.