You’re severely underestimating the budget Meta can throw at this. Mastodon/Lemmy/etc. right now are largely volunteer-run as opposed to full-time employees.
But they can easily implement Lemmy-like features on it or make another sister-app. It isn't hard to bruteforce such things when you have that much money and developers
I wouldn't underestimate them though. After all, they own some of the biggest social network platforms on the globe and have the formula to hook people up down to a t.