"Waiting time in outpatient clinic"

I attended the Ophthalmogy  clinic at Ayr hospital for a 3.20 appointment. At 3.10 I was seenby a nurse for a quick vision check and then asked to take a seat in the corridor. For almost 2 hours i waited as all the other patients several of whom arrrived after me were seen. Doctors and nurses were now leaving , switching off room lights and I was beginning to feel unwell in the heat. 

I then asked one of the remaining nurses if I had been forgotten about as I was now sitting forlornly alone.watching the cleaners working around me She told me I was last on the list. I was seen at 5.10 pm

Why give an appointment for 3.20 when it seems that it was obvious I would not be seen before 5pm?