Clerical celibacy is not a doctrine. It is not a divinely revealed Truth. Rather, it is a policy of the Roman Church. If it were a doctrine, then how could Rome consider itself in Communion with churches that allow married men to become priests?
Because clerical celibacy is not a doctrine, but rather a policy, it is subject to modification should the circumstances require it. Whether or not those circumstances are present today is another question.
Clerical celibacy is a discipline not a policy.