It's like they took IRC, saw it worked for businesses, and were like "how can we fuck this up, slowly, to destroy the very essence of what made chat channels useful in the first place?".
The issue for my Slack workspaces is that they are not noisy. So what happens is, people (inadvertently?) make threads, which then turns off notifications about that conversation for everyone else, therefore taking them out of the loop. And because the room is not noisy, they may not notice that they've missed the conversation until hours or even days have passed.