Since we can switch any time enough folks feel like moving over some of the major group threads to something else, how are we locked in? I can't really think of any time I didn't do nearly all of my communication over one or maybe two channels. In the 1990s, 95+% by landline phone. Then ICQ + Phone. Then SMS. Then WhatsApp.

I also do 95+% of my driving in a single car, and 95+% of my text editing in a single program. 95ish% of my browsing in a single browser. Not locked in to those, either—in all three cases I've switched before without difficulty, and likely will again. I have no idea where the lock-in notion's coming from.

"Locked in" doesn't just mean "I use a single thing for everything".

It means that switching costs are high. With the exception of losing chat history (which I was surprised to find most people don't seem to care about), switching costs between chat platforms are virtually nonexistent.