Should not a universal church have universal rules?
The Catholic Church actually consists of a number of local churches, which have historically different cultures, emphases and rites.
The Western Church has erred in the past by giving short shrift to the Eastern Churches which are in communion with us. That's being corrected, I think.
Moral rules and basic doctrines are, of course, all the same and always will be. But there's no binding reason why all customary and disciplinary rules have to universal, no.
You wrote: "Should not a universal church have universal rules?"
Yes, and it does. Here is the universal rule of the Universal Church on priests and marriage. Once ordained, they can't marry. That's the universally observed rule. It is observed by all Catholics and Eastern Orthodox (as far as I know).
Beyond that there are different rules according to the particular churches. Neither Catholics nor Orthodox have married bishops. But only the Orthodox choose their bishops exclusively from monasteries.
Still, particular churches have their own particular rules about celibacy or married clergy.