A normal internet user may also have a custom domain, like 90% of all companies do.

A normal internet user may also be in a country where ".com" is not the main TLD.

Granted, .pizza is unusual, but there is no valid excuse for not supporting it, and systems that fail to use it likely also fail other completely "normal" email addresses due to other invalid email validation like assuming a TLD has one dot, that an email address has a certain arbitrary max length, or because they failed to enumerate even common TLDs.

The only proper way to validate an email is to send an email to it.