Why do many subreddits plateau at 60–80k members, and how can we build long-lasting growth?

I’ve noticed a pattern across several subreddits: they grow pretty quickly at first, sometimes hitting 60–80k members, then growth slows down and the community plateaus.

I’m wondering:

• Why does growth often stall around that point?
• How much of it comes down to the topic being too narrow vs. something about how the community is managed?
• What should moderators and community builders focus on early to avoid or improve this slowdown?
• More broadly, what are the key factors you’ve seen in subreddits that remain active, engaging, and long-lasting?

I’d love to hear what’s worked (or not worked) from your experience. Thanks!