Why did I fail on some US. Online shopping websites?

That’s because some US. E-commerce websites are for US residents only. These website will block foreign IP addresses, and even including proxies and VPNs.
So what you have to be needed here is the US. Residential IP address. This US. Residential IP address is connected to real physical devices inside USA, which makes it different from most public proxies and VPNs. The next thing for you to do is to find some US. Freight forwarder.