Why doesn’t the university just expel them? I imagine any western university would. Something like “we respect freedom of expression, but glorifying violence does not align with the standards we set bla bla bla”
You touched the root problem.
The reason why the university hadn't expelled them is because the university
supports them.
How do you think they have become student "leaders"? Anyone who knows how the student elections work is that the University is often supporting these processes.
And how did these students got leaders? Because other students voted for them.
So this means that the whole university and education system is rotten to the core. They have brainwashed the younger generation to such a degree that these "students" openly support terrorists with implied support from the education system.
This is the root cause. The education system is corrupt and rotten to the core. This is what happens when you let these tumours to grow uncontrollable.
Lets see how China deals with the entire younger generation of HK being brainwashed...