I am sorry to hear that your appointment was rescheduled.
Unfortunately, these things happen, as sad as it sounds. Gynecologists or midwifes are the one delivering babies and when they have to deliver, they have to go. There may be others on duty in the office but they have their own clientelle as well. I remember sitting over an hour or more a few times for my appointment as mine was out delivering a baby.
I suppose you can look at it the other way around. If you were going to deliver your baby, imagine if you had to wait a few hours while she saw patients at the office.