Groups of primates grow up to only a certain rough number, depending on the species. After that communication problems, jealousies, etc, prevent the ones on top of the pack from being able to manage the situation.

As someone who barely uses social media, I don't really understand what someone means when they "communicate" with 60,000 people. I envision a guy standing on the concert stage with a megaphone and 60,000 below him.