I think network effects are much less pronounced with microblog platforms like Twitter, Parler, and Mastodon — most people sign up for these platforms to follow

I think network effects are much less pronounced with microblog platforms like Twitter, Parler, and Mastodon — most people sign up for these platforms to follow a few big accounts with orders of magnitude more followers than the average account. There’s no detriment to flipping between a Twitter and Mastondon/Parler account depending on which big accounts you want to read. Contrariwise, people sign up for Facebook to socialize with their friend group as a whole. An alternative platform with only a handful of your friends would be pretty useless. Worse, having your friend group split between platforms would completely prevent being able to socialize as a group, defeating the whole point of the platform.