It’s only almost all if you only interact with the millennials or younger. Pinyin is an IME for Mandarin. If you aren’t fluent in Mandarin, chances are you use voice input or stroke typing.
Why shouldn't it be mainland-centric? Mainland China is 99.5 percent of the population of China. That's like refuting a claim about Americans by calling it "a very non-Pennsylvanian view".
Because China is not the only place where Chinese languages are spoken. There’s more than 10 million ethnic Chinese in Southeast Asia alone. And it’s not only a mainland-centric view: it’s a mainland–Mandarin speaking centric view.
