You can change your App Store region and load those apps if you want, even if you live in china. You can even have apps from different App Store regions be loaded side by side (e.g. Facebook and xiami).
You need to be able to pay from a US credit card in order to buy anything from the US store. Which is out of the reach of ordinary Chinese. I often help my Vietnamese friends buy apps from the US app store for the same reason.
Yes, but for the free apps it doesn’t matter; it really is something that is useful. Most ordinary Chinese aren’t going to be interested in those apps anyways, like they wouldn’t be interested in side loading.