They are "paid for time." True, they are expected to provide some additional value in the span of time that they are paid for. I'm a service professional and my service is metered by time. If I call on the client, the clock starts running the moment I walk in the door, even if I'm sitting in the lobby waiting. Of course, I'm expected to provide some value during the time I'm there - I don't just get paid for showing up. And neither do providers. And I'm very protective of my non-billable time. I provide a free 15-minute telephone consult, that's it.
I have so many of the same frustrations that providers do - time wasters, no shows, people who think I charge too much, people looking for freebies, etc. that I'm in complete sympathy with them. If I weren't so old, it could be my night job.