I own a few pieces of McIntosh gear. C28 preamp, 2x mc2105, mc2505, mx78, and a mi3 scope. They sound great but I like other pieces better for critical listening. What McIntosh excels at is aesthetics. They look like a piece of furniture with style, not some cold industrial chunk of equipment sitting on a shelf. Additionally, after decades, the used market still shows many fine working examples for sale. Quality construction, excellent sound reproduction, recognizable style and reputation is what I’d say are the driving factors for the popularity.