I am proposing this as a hypothesis.
Loudspeaker manufacturers have a problem that as loudspeakers got better, in that they had a flatter frequency response and lower distortion, they became similar sounding, and thus harder to distinguish in quick dealer demos and HiFi shows. In order to stand out, they had to be different, so frequency responses became more ragged, with excessive HF (listen to all that detail and air round the instruments) and LF distortion (listen to that bass thump). This has given rise to something of a 'signature sound' for manufacturers, but consequently the technical performance is actually worse.
I don't have proof of this, but as evidence, I propose the frequency response of some very expensive 'boutique' manufacturers like Boenik and Zu, and even some established manufacturers like B&W.
S
That makes sense to me, and I've actually also had the same thoughts. Wilson Audio is another example. They make some of the most expensive speakers in the world, but measure not so well. I've listened to Wilson Alexia in two different shops and liked them quite a lot, but I didn't compare them to anything, so it was difficult to judge them. I think I like a certain sound signature, and Wilson has been voiced that way.
I did, however, also listen to Wilson Yvette right after I had listened to another brand (GoldenEar) that I found a tad bright. The Wilson Yvette were not bright at all, but very dull. I ended up buying GoldenEar, just another model.
In any case, this "voicing" of products is not constricted to speakers, but also applies to amps, CD players, phono cartridges, etc.
While some hyper expensive products do measure extremely well (such as the phono preamp by Boulder, which was reviewed in Stereophile), then products like the phono preamp by Ypsilon that Michael Fremer used to use, the Zanden 5000 CD player that he called the best CD player he had ever heard, and loads and loads of hyper expensive phono cartridges, like Lyra, Zyx, Red Wing Sparrow, etc. are voiced a certain way, which is exactly why they are so expensive - you don't pay for accuracy but for a signature sound.
With phono cartridges it is impossible to make a completely flat frequency response, but the Goldring Elite and the Nagaoka MP-500 are surprisingly flat, and they're not all that expensive compared to the ones the audiophiles rave about. But hardly any "self-respecting audiophile" would choose the Goldringe Elite over a more expensive and less accurate option.
The only somewhat more expensive phono cartridge I've come across that is surprisingly flat is the Dynavector DV XX2 (€1500), and then the Dynavector DRT-XV-1T, which is around six times as expensive at €7000.
Some people do try to choose technically good products, but many like a certain sound and "sounds good to me, therefore it must be better quality, and I will scream at anybody who claims the opposite" has become the slogan for many people.