Doctors, dentists offices why do their rules apply?

I’m sitting in the lobby of my new dentist office. She won’t be my dentist for long. I’ve been considering why the rules of customer service just don’t seem to apply to the medical profession. My belief is that the entire system is screwed up but I do have a little bit of power here. I can do the same thing I would do in a commercial setting, take my business elsewhere. Sure, this doc is the closest to my house and they take my insurance, but she is not the only dentist.
I don’t understand how it is considered acceptable to fine me for changing an appointment or for showing up 10 minutes late (I’ve done neither but have been told of the comsequnces twice) but the can change my appointment and make me wait for an hour with not even an apology.
That was the last visit, this one was changed (without input from me) from 11 to 11:45. Then I got a call that I could come in early….at 11 if I’d like to be seen early. I arrived at 11, got in at 11:25. Huh?