Good question. My take is that it’s a “Roman thing” meaning that they had to come up with something. That said, I don’t agree that the UGCC should be considered a “Patriarchate” at least not officially. My objection (as I’ve said in previous threads) is on principle, not at all on practical grounds. There are, traditionally, five Patriarchates that have been recognized by Councils. Neither Lviv (nor Kiev nor, for that matter, Moscow) is among them. As I see it, the proliferation of “national Patriarchates” among the (for the most part) Slav Byzantines is a problem.
OTOH, it also kills me is that Rome gives the same title (Major Archbishop) to the head of the Syro-Malankara Church when, in fact, there is a perfectly legitimate title (Catholicos) which is actually traditional in the Syriac Churches. (Of course “Catholicos” is not a Byzantine concept, and while it might work in theory in the case of the UGCC, they (the UGCC) would probably reject it because it’s not a Byzantine concept.)