From my understanding, this is because neither of these are actually true "Chinese" dishes,. Ginger Beef was "invented" by a Chinese immigrant in Calgary in the 1970s [0], whereas the westernized Orange Chicken is actually a variation on General Tso's chicken, which was invented/popularized in New York in the early 1970s [1].
[0] https://web.archive.org/web/20090330125905/http://cbc.ca/new...
[1] https://en.wikipedia.org/wiki/General_Tso%27s_chicken#Name_a...