Earlier quoted context omitted.
The author specifically calls out ephemerality as a feature of IRC. If it's easy to get history people will assume everyone is reading what they're typing. This would make people feel obligated to play catch-up every time they miss some messages due to being AFK or in the zone. By making history hard to obtain, IRC simulates real-world conversation -- you're either in the room or you're not.
If I wanted real world conversation, I can drop into a conference call, I don't need IRC for that. Chats in organizations are specifically for when email is not realtime enough but it's important to keep a record of the conversations for some time.
This varies immensely per organisation so it's always kind of dangerous to generalise like this. For example: The use-case you quote does not align with my experience of (bigcorp) chats at all.