You’d have to get those countries to agree on a common set of governance rules, and inevitably some bloc of countries would eventually fork and go it on their own because they want a different set of rules (e.g. mandatory biometric data, inability to update passport data like gender, etc). I’m not sure it solves any problems that the diplomatic system doesn’t already solve.

This also ignores that the costs and delays associated with passports are frequently the point — you can’t have a corrupt official ask for a cash payment to “expedite” your passport / visa application if it’s fast to begin with, and doling out those kinds of patronage positions to the right people is often how you build a winning political coalition domestically.