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Humans aren't perfect but they're reliable enough to be trusted with customer service work. Humans (generally) have a desire and need to keep their jobs and therefore hold themselves to a high enough standard of performance to keep their job.

And maybe employment contracts have language that offloads liability to an employee if they go rogue and start giving away company resources. Chatbots aren't accountable in any way and we don't know yet if their creators ever will be either.

And disclaimers are used in lots of contexts too.