People get really annoyed that they cannot find answers to previous questions, and if you have q&a website to get around that, your just moving the chat goalposts around. Not to mention its a higher friction process, so people go ask questions anyway on the company slack.

Also screenshots are a thing and easy to do in secret impulsively, recording stuff when your talking in person has a much higher threshold, and far less people are typically listening.

Also once you get to a certain size, there are legislative retention requirements and legal holds.