In my very limited experience this happens when managers (above team leads) insist on being present in chat rooms. No offense to any manager in this topic, I know that you mean no harm in 99.9% of cases and that you do want to make things better, but honestly your presence creates a chiller effect. Jokes are no go, because who knows, maybe this one will be interpreted badly. Local questions are no go, because you can't ask them during work time (he's slacking!), you can't ask anything which can even remotely be treated as improper. Can't show that you lack knowledge in things which should be obvious, can't banter about colleagues or about work in non-positive way. And the list goes on. We have a chat with 100 people which started as a meme and joke one, a lot of people were posting funny stuff there. Now the last meme picture posted there in mid october, and the second to last was in august. And the only people posting there at all, even sirius stuff, are the 3-4 teamleads very close to the management. Same shit in the chat of immigrants, we have a quite a few semi-permanent relocants on the projects, but manager is not one of them and is still present in that chat room. No one posts there, everyone talks either behind the scenes (because there are a lot of questions for people in new country) or in the independent big chats outside of the company.

And again, it's not like our managers are bad, quite the contrary, they are very good professionally and personally. And we don't have layoffs. But people still won't talk in the presence of even mid level management, it's an instinct of sorts I guess :) .

PS: this is only about informal optional chats. All work chats are never hidden or avoided. We divide them by program, Slack for work and Telegram for fluff.