I think the reason guitarists like old stuff is because of the nature of creativity.
Hear me out... try this thought experiment.
Alright, I want you to create a fictional being, a monster of sorts, that is completely original. Do it, and draw a quick picture of it.
What does it look like? Do it have an eye/eyes... something to see with? A mouth? Teeth maybe? Does it have legs or arms? Skin/fur/scales? Does it look like an amalgamation of several animals?
It's actually incredibly difficult to do this task and to come up with something that is NOT derivative. You see it even in real examples of this... a dragon is just a cross between a lizard and a bird, a minotaur is a cross between a bull and a man, a centaur is a cross between a horse and a man. Even the popular conceptual of aliens, the little grey men with faces that are more or less just like ours (two eyes, nose, mouth, etc).
Most creativity is derivative. When we see innovation, it is usually a co-incidence. Example: The emergence of distortion was not some guy going, "You know what would sound cool... this sound", instead, it was just people needing to turn amps up loud to be heard and they became overdriven. Even the emergence of the electric guitar was a practical thing and not creative. Every style of music in the last 1000 years has been a modification of previous styles, rather than something new.
So what's the first thing someone does when they want a heavy tone? They do what other people did who produced heavy tones they like. What does someone do when they need a cool clean sound? They do what their heroes did for clean sound. We copy. Even unconsciously... we might not buy signature gear but there's a reason why we gravitate towards fender amps and strats/teles for clean tones and humbuckers/marshalls for dirt... it's because our heroes did and we do not think in an original way when trying to create something new.
This is also why it's so hard for new producers to enter the market. What is the number one thing a new builder can do to get people's attention... to make them aware that actually, this new product can do these things too? That's right... get one of your guitar heroes to play it. See; Mesa Boogie.
Honestly, if Clapton, Page, Beck, etc... started playing multiscale guitars with active pickups and transposing tremolos, made out of space-age materials... then everyone would start believing that those designs were optimal.
The next big innovation in guitar design will be due to engineering necessity, not the open-mindedness of guitarists. After all, didn't Fender design only come about because Leo wanted a way to cheaply produce and assemble guitars?