Subscriber numbers mean little. Take a look at the trend for the posts per day and comments per day graphs. They’re far more accurate indicators of the level of engagement actual users are having with reddit.
I’ve just checked for 10 of the subs I used to subscribe to, 2 of which have over 30m subscribers - all of them have the same downward trend in terms of posts and comments. I’m not saying reddit is in trouble but less new content is being created and that which is is being talked about less, eventually that will take a toll.