A chatbot produces text. Whatever it says, the worst outcome is that a person reads something wrong. That is not trivial — wrong information causes real harm — but the failure is contained to the conversation.
An agent calls tools. It updates records, sends messages, issues refunds, provisions access. When an agent is wrong, the consequence persists in systems outside the conversation, and may not be noticed for weeks.
Everything else follows from that. An agent needs a permission model, an audit trail, confirmation on destructive operations, and someone to have asked "what is the worst this can do if fully compromised". A chatbot needs good retrieval and a sensible tone. Teams that build agents with chatbot discipline are the ones most likely to have incidents.