Why are most High End Amps class A

Good advice from Stanwal.

Making sure the amp can drive the speakers properly is the most important factor. Most else is subjective judgement regarding what sound best.

As Stanwal wisely states, listen before you change. I have owned a McIntosh 2105 for 10 years, and during that time also owned a Mac MC 300 which I sold after 3 years to buy a Pass Labs X250.5. For most efficient speakers, at modest volumes , that amp will run in class A. I used it with 3 different speakers, and for my taste, the Mac 2105 was better in all aspects. The point of course is that you may feel differently, but do not make the mistake that I made and buy on the opinion of others and their taste - try it first.

Class A amps run at full power when idling. So if you really want a dual use machine (home heater, and amp) then go for pure class A.
I have a small 50w 'class A' amp, and love it. I would never buy a big class A because of the heat, and strain on the electrical system.

Most Class A amps are higher priced, and not necessarily higher end. Due to the high heat output, most class A amp will need higher quality parts and much more expensive case work to dissipate the heat, thus resulting in a higher cost.

Class A amps will also waste a lot of power and run up your power bill, so be sure it's worth it.

Personally, when the time comes to look at a new amp, I will be looking towards Class D, which is the opposite end of the spectrum in terms of efficiency and value from class A.