“Their theology and liturgy is identical.”
If that’s the case then why 27 plus different denominations? Why not just “one” church?
They are not "denominations." The Orthodox Church is a communion of churches, just as it was form the beginning. They all believe, teach and practice the same faith -- in their own culture and language. Just because the Bible exists in multitude of languages doesn't mean there are multitutde of bibles. There is only one Bible.
Protestant denominations differ in theology and practice, as well as organization and leaderhsip; some allow women clergy, others don't. It's apples and oranges. I can walk into any Orthodox Church and know exactly which part of the Divine Liturgy is being sung and what is going on, regadles sof which language is used. I know that for a fact because in my six years in Japan I attended the services in the "Nicholas do" Orthodox Chuch of Japan Catedral in Tokyo. Everything in that church was the same as in any other Orthodox church.