Why do I need a prescription for buying a new mask ?

I've been using cpap for a couple years. I now feel the need to shop for an upgraded mask. Why would I need a prescription to buy a new mask ? Am I misunderstanding this ? My experience often is that health industry forces you to make an appointment for this requirement. An appointment usually is scheduled out 2 months. I hope I'm misunderstanding this, cause otherwise it makes my head explode due to exploitation economics.

It is a US regulation that requires a prescription. In Canada we only need it for a machine, not the mask or other parts. The original prescription for your machine should work as a prescription for a mask. The other way around it in the US is to buy the mask in two parts; the headgear, and the mask. Then you put it together when you receive it. I recall at CPAP.com the cost of buying it in two parts is the same as buying the complete mask. The issue might be getting the return insurance when you get it in parts...