I have the suspicion that the CCP is very scared of knowledge of Tiananmen spreading, not because of the amount of victims (fairly low by Chinese standards and for how large the protests were), but rather that they are scared of the knowledge spreading of how much popular support the movement had and of how widespread it was. Most soldiers were also unwilling to attack civilians, so army divisions had to be brought in from far away and the soldiers had to be subjected to misinformation to goad them into attacking civilians.

This wiki article goes over what it took to suppress the protests: https://en.m.wikipedia.org/wiki/People%27s_Liberation_Army_at_the_1989_Tiananmen_Square_protests_and_massacre

Afterwards the CCP took steps to ensure that next time, the army would be more loyal to the government: officers who had no qualms with attacking civilians were rewarded/promoted, and those who had not executed their orders were purged. Dictators need immoral people to execute their orders.