That's the month it happened, so that's the month people post about it, meaning it's also the month it's removed and people cry foul.

Tiananmen Massacre anniversary is June 4, so there are multiple posts about it (which is great), and a couple of those posts get removed (usually for really obvious violations of sub-specific rules), and someone sees that and cries "Reddit is censoring! CCP shills!"

It's a damn Reddit tradition at this point