I think when you've got a government that's had insane crackdowns like this before escalate from other situations, even though they were not as "innocent" as the student protest for road safety, but their protests from 2012-2013 in the run up in their election show that they'll just abduct people never to be seen again... it sort of just becomes an instinct for governments that do shite like this. The brutality sends a message.
It's like Iranians who were protesting the recent presidential elections & more recently, the protests because of the inflation & food crisis (which have started popping up again actually). Once the protests grow to a certain point, they seem to have their will to protest beaten and shot out of them, with the leaders mysteriously disappearing and turning up years later released from Evin prison (if they're lucky).
Seems to always make people think twice about taking to the streets about their legitimate grievances.