I've ran into this even in my limited advertising on meta - they actaully want you to use the actual individual's facebook account to manage the ads accounts, even on behalf of the clients through the agency.

This is kind of insane behavior but when you remember that google actually supports enterprise domains and SSO and facebook has very little of that - or relatively little - it makes sense. If you are personally banned from facebook for whatever reason, you cannot have a business account under another email - once you validate your identity it regurgitates the ban.

Despite this being an obvious antipattern to security it is very much by design for meta.