That’s true from our perspective, but not from someone like Cory’s.
The trap he writes about being stuck on these platforms is because he doesn’t just have friends and people he follows on these platforms — he has an audience. And closing his Twitter or Facebook or whatever would mean leaving large audiences that he has built up behind.
Cory stays on those platforms as his own version of the (justifiable, but regretful) compromise he writes about companies making. Better to stay on those shitty platforms and continue to reach people than abandon both the shitty platforms and his audiences there.
That’s why he doesn’t want to put effort into building an audience somewhere that might force him into the same compromise again.