Seems to me the most likely explanation of the musicality of tubes is in the art of our mind's eye.
There’s also perhaps the “ hip” or G-Wiz or newness factor.
Similar to how it’s working in the vinyl revival: Much of the vinyl revival is driven by Young people who would never experience vinyl playback and turntables. To those of us who grew up with vinyl it’s old news, a technology of the past. Two young people it’s a new technology, or at least an entirely new experience, the differentiates it from the status quo and what they are used to, and may have become mundane to some.
Similarly tube amps seem to still be going strong in the audio community. I can see it. I think in some of the reactions of younger audiophiles when tube apps are discussed on the Reddit forums are on YouTube.
I’m 60 and I did not grow up with tube amplification. Solid state was all I knew.
One day, in the 90s , a fellow, audiophile coworker came in and just started murmuring “toobs”. “Toooobs.”
I asked him what he was going on about, and he explained he’d been converted to tube amps in his system. I went to his place and got my first introduction to tube amplification (Conrad Johnson amp if I remember properly).
For me, it was a new thing, and really cool. Both retro and refreshingly different. And I think there’s still a bit of an element of that and why I enjoy owning the tube amps. I love the looks and the vibe and the attachment to the history of audio, and also it’s a bit different than yet another standard issue box solid-state amp. When I am lent solid amps by my pals, they do nothing for me in terms of looks or vibe, they are just another utilitarian metal box.