> nobody uses them because you'll never be able to use anybody else's keyboard
I doubt that's the main reason, and it may be unwarranted as I say below. Personally, I thought it would take too long for me to be able to type as fast as in QWERTY. Fortunately, I was wrong about that too.
I learned the QGMLW optimized layout from Carpalx (linked above) about a year ago. I trained on https://keybr.com and then on https://typeracer.com for a few days and in less than a week I reached 70wpm. I stopped training shortly after and now I can usually reach 90-100wpm. Not particularly fast, but I'm not any faster in QWERTY, and I believe I could get faster if I trained more.
Even though I almost never type in QWERTY anymore, when I do I'm still just as fast as I used to be. I never learned to type in QWERTY "the right way", though, and I suppose this is actually what keeps me from confusing the two "modes". Whenever I try to keep my fingers on their "appropriate" keys (like a properly trained typist would), it's like my brain switches to "Carpalx mode" (since I did make an effort to use the right finger positioning to learn it). It's kinda like switching between thinking in my native language and English - I can think in both, but it doesn't "feel" the same, and I'm more likely to confuse the two where they overlap more. Pretty interesting, really.
Yeah I did the same thing but I learned colemak. I never learned to touch-type qwerty, when I learned touch-typing I switched to colemak. I feel like it made things easier as I didn't have bad habits to fall back on.
I can still type qwerty but I'm not very fast at it (I never was).
QWERTY isn't as bad as people make it out to be, and Dvorak isn't as good as people make it out to be.
There are keyboard configurations that are better than both, but nobody uses them because you'll never be able to use anybody else's keyboard.