Actually, ironically, knowledge of the Tiananmen Square WAS indeed suppressed in the west. What we know is the single guy standing in front of the tanks. What we in the west did not know is that, in fact, the great majority of protesters were workers being oppressed by the "free-market" reforms being implemented at the time. In other words, the protests were basically against the oppression caused by the new westernized-style economy.

This was (is) suppressed in the western media because it goes against our narrative that protesters were fighting for democracy, when in fact they were protesting against the oppression created by the same system that we so much value.

EDIT: I forgot to include sources. Check the book "What Does China Think?" by Mark Leonard, and look for essays by Cui Zhiyuan, a Chinese philosopher who was part of the Tiananmen protests.