Harmony is the OS by Huawei.

In the US, iPhones and Samsung phones are highly subsidized by phone carriers. Motorola to an extent (mostly low end models). Also, Verizon blocks other phones from their network. Check what they sell on their site and you’ll see what’s available to buy as an American. Americans have much less disposable income, so you’ll notice there’re huge subsidies for consumerism; Americans have to be goaded into spending money with discounts or else they won’t buy; it’s a cultural thing.