How long have these subs existed? I doubt that either one grew by 150k users within the first week after being created, and the "reddit exodus" has only just begun... if this trend continues, lemmy.world won't be at "just" 150k anymore in a month or two.
Not to mention a lot of those subs were "default subs" (subs that new users were automatically subscribed to when they signed up for Reddit) before Reddit got rid of those.