Good grief...is there a point in even having a Traditional Theology forum when it seems like every thread is filled beyond capacity with "I love Jesus, but hate religion/church"-type posts? Go away already with that. You mental midgets already have literally the rest of this website outside of the confessional forums on which to spread that particular poison.
Anyway...surprise, surprise, I agree with the only other OO person here that the answer is that these groups all have their own histories. So while it's possible to just say "Christian" (after all, Protestant, Catholics, and Orthodox are all Christians), it doesn't tell the whole story. And so being Protestant, Catholic, Orthodox, Nestorian, etc. means not just aligning your spiritual practices or theological beliefs with what is specific to whichever particular group you've aligned yourself with, but also imbibing their historical views, philosophical underpinnings, and so on. For example, as much as we love them as people and as fellow Christians (even when they often don't see us in that light), I recognize that I would not be a very good Oriental Orthodox Christian if I were to accept without question and adopt as my own view the standard Chalcedonian take on Christian history, just as the Chalcedonians usually avoid distinctly OO historical figures, including historians like Zacharias of Mytilene, Sebeos the Armenian, Jacob of Edessa, Joshua the Stylite of Zuqnin, etc.
And these things are perhaps not as removed from theology as we'd like to think they are. The Maronites, for instance (an ethnoreligious sect of Catholic Christians from the Levant), have as part of their liturgical calendar (I don't recall when) the celebration of a large group of martyrs of their faith who their tradition says were martyred at the command of St. Severus of Antioch, the Syriac Orthodox (Oriental Orthodox/non-Chalcedonian) patriarch of Antioch (512-538). There are some issues with the historicity of this account, to put it politely (see Matti Moosa's book The Maronites in History, 1986), but the important thing to know in the context of this celebration is that the Maronites are a traditionally Syriac-speaking Chalcedonian people (i.e., they accept the Christological definition promulgated as orthodox at that council in 451), and hence can be distinguished on that account from the other major Syriac-speaking population of the Middle East, the Syriac Orthodox. (Newer groups of Syriac Christians aligned with Rome don't have as much history, or their history is ultimately rooted in different conflicts, as is the case with the Chaldeans in Iraq, who arose from a 16th century dispute within the Nestorian Church, which both Chalcedonians and non-Chalcedonians anathematize.)
So their history is defined by the theological turns they've taken, same as anyone. A virtually identical paragraph could be written about the Coptic Orthodox Church and its people, the Armenian Apostolic Church, the Georgian Orthodox Church, the Roman Catholic Church (Latins), etc. Faith and history go together for everyone but those who claim to be "just Christian" and hence cut themselves off from the historical reality of what that means, from the earliest days when St. Paul was writing his epistles to the churches at various locations down to our own day.