How do you handle binationals who might not have the same details (or even name) on each of their passports?
You can always get around identification requirements, for example by purchasing a fake passport in this case. The idea is to increase the cost/friction of doing so as much as possible.
A fake ID is a lot harder to get your hands on than a new email, burner phone, etc.
1 passport = one human
Yes, this does mean that dual nationals can have two separate human accounts. But it’s still better than an infinite number of accounts, which is the case for social networks right now.