Most guitarists are radically old-school and won't even look at an amp that doesn't have a row of 12AX7s / 6L6GCs / EL84s visible in the back. The mindset is pretty much "If vacuum tubes were good enough for Chet Atkins, Les Paul, Eric Clapton, Jimmy Page, Jimi Hendrix, Stevie Ray Vaughn, and Eddie Van Halen..."
How can you argue with that logic?
You don't, because it is not logic.
Rather than "If vacuum tubes were good enough" it is "It must have been the valve amplifier and the high-capacitance spiral cords that made the old guys sound so good. If I only buy something vintage or vintage-looking I'll get better tone."
It is convenient to disregard both "10000 hours of practice" (even if that figure is
debated ) and the fact that back then you really did everything by hand, so there was no way out of actually being good at what you did. Also, recording was expensive and tightly controlled because of that, so only the most selected were actually recorded.
Then, naturally, there is a
market for these things that makes no effort at emphasising the virtues of practice or talent.
On the subject of thermionic technology,
borderline deception circuits are what is being done today, because people so desperately want Old Gear.
Having written all this, and observed the fact that the new gear (by which I mean stuff built the last 25 years or so) is so radically better, on average, I still have the desire to build a valve guitar amplifier, but that is because I want to learn how it is done while spending lab bench time with the intended user, Middle Boy, not that I think he'll be any better purely from thermionic amplification. It might do wonders for his motivation, though.