They need a place to be, they need to get hired, trained, managed and all the associated general costs of employment (hr, payroll, etc). They need equipment, there's monitoring, evaluations etc.

Then you also have to pay them regardless of whether someone calls.

I edited my comment above and explained, that $20 is an amortized cost representing everything that goes into picking up that phone call.

While I agree with TFA's point that forcing a chatbot isn't a substitute for just having the info available, organized and searchable, the answer to your specific question is that the fully burdened cost of a trained support center human includes a lot more than their gross hourly wage. There's recruiting, interviewing, hiring, training plus space, desk, computer, phone, IT, HR, health care, vacation, sick days, insurance, employer's share of employment taxes.

A rough rule of thumb is the full burdened cost of an hourly office knowledge worker is two to three times the gross hourly wage.