It literally wasn’t added after the schism. Catholic means universal. That’s why Romans, Orthodox, and most Protestants all say “I believe in one holy catholic apostolic church” in the creed. Anglo-Catholics and old Catholics and orthodox Catholics are all *not* in communion with Roman Catholics. Romans have never owned the word Catholic they’re just the largest group.
Discussion
📝
It's like how people from the USA are called "Americans", but Canadians and etc. are also Americans.
I try to clarify with capitalization. I'm an "orthodox Catholic", but not an "Orthodox Catholic".
That confuses people, too, as I'm using "orthodox" to clarify that I'm neither trad, nor liberal.