I used to work in IT support before becoming a librarian and my experience confirms this. Most (but not all, there were many pleasant people who called the IT desk) were in a sour mood when they called, making it hard to keep my own sunny disposition. When people come to a library desk, they're excited about any help they receive.

Extending your second paragraph, when people interact with the IT desk, they're trying to go from a bad state up to their base state. When people interact with a library desk, they're trying to go from a base state up to anything above that.

I can see what you mean, we ( = professor an I speculating) thought that would be factor. OTOH, people go to the doctor only when they're sick, which is also a bad state, but being a doctor isn't considered a thankless job whereas IT is.

Just speculating here, but I think it has to do with how a lot of people seem to look down on IT, and tend to blame them for their problems. With doctors, the people tend to look up to them, and don't blame them for their illnesses[0].

> when they called

I'm pretty sure this makes an enormous difference as well, btw, compared to face-to-face communication.

So we got three examples of service work, where the interaction with the customer completely shapes the experience for everyone involved.

[0] ignoring malpractice cases and such, but that's after treatment, not before.