You need to distinguish between the McIntosh tube amplifiers and solid-state amplifiers. The tube amplifiers are where they shine. The reliability plus the performance is what makes mcintosh tube amplifiers very desirable. Solid-state amplifiers are comparable to most other solid-state amplifiers as most solid-state amplifiers are pretty reliable.
Plus the resale factor is a huge component of all this. Other amplifiers tend to be way overpriced as demonstrated in the used market where after two or three years you were lucky to get 40% of what you paid. And very difficult to get rid of most other brands.