It's surprising how few Chinese people study in America. With a population 1/14th of America, Australia has 150,000 Chinese students.
The US entry refusals should be familiar fare to Chinese citizens though, as their Govt employs stochastic enforcement all the time, including for censorship and as part of trade disputes.
It sucks for the individuals, but this really isn't about them, it's about the CCP and it's ongoing campaign of industrial espionage and global surveillance.
It is likely a number of 'students' were also part of the diaspora surveillance network, routinely reporting back about the behaviour of overseas Chinese citizens and especially minorities.