The mods who left were quickly replaced.

Most mod teams didn’t leave. They made an example of a handful of especially rebellious mod teams, albeit I believe in most cases they had a quisling near the bottom of the mod list contacting reddit to tell them they would happily take over.

But there’s a difference between doing that dozen times, and having to do that a thousand times.

The subreddit mods had all the power. If the top mods of all the communities that blacked out just removed all mods and shut down the subreddit, it would’ve been chaos on Reddits end.