Is that necessarily a bad thing though? Two things come to mind:
Do I want the kind of user here that’s willing to sign up for Facebook’s new social platform?
Do I want +100 million users here flooding every interesting discussion with thousands of comments to the point that my reply is immediately going to get lost in the flood of new messages?
I wouldn’t be surprised if even now with our 6.5 million users the quality of discussion here is far greater than it is on Threads with their 30 million users. Obviously too little users is a bad thing but I imagine there can also be too many. Back in my reddit days I much more enjoyed the more slow paced niche subs than the popular ones with 10 million subs. Replying to AskReddit thread with 1000 messages is a complete waste of time. No one is going to read it.