> 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.
