As long as China isn't breaking any WTO rules, they are free to block internet services and apps. If other countries aren't happy with this, they should change the WTO rules. If WTO rules are being broke, then clearly those rules have no teeth.

Why would China block things? Various excellent reasons are discussed in this thread, and they all boil down to political and commercial.

Are the Chinese people harmed? I would argue not. None of these "services" do anything really important nor irreplaceable. Most are just new spins on ancient tech like email and FTP, and the new versions that are blocked don't really have any differentiating features compared to what is available locally. The feature that is new is Digital Identity.

And so my final thought is that they are playing a long game with respect to digital identity - which is the long game of most of these blocked services. In Cyberspace, am I going to be Chinese or American? I aM not Chinese, but I expect that most Chinese will want to also be Chinese in Cyberspace, and so the Chinese government is fulfilling that desire.