A you tube video by the engineer guy claims that Dvorak didn't catch on because it's only 5% faster. (I can't go to you tube here to link to it).
When I first decided to get away from hunt and peck I learned Dvorak on a Kinesis ergo keyboard but eventually I used the shareware program Stamina to learn Qwerty touch typing so I can be fast on any ordinary keyboard that I come across.
I would completely believe the 5% thing. And that may be optimistic, given that many people have decades of QWERTY use. It's not like 'learning' a new layout is just flipping a switch...it will still take tons of use to develop the same second-natured typing ability.
DVORAK was obviously conceived by engineers. 'Put the statistically most-used keys on the home keys! BRILLIANT! It will be 400% faster!'
Only, uh, nope. Not at all. Keys not on the home row are still not hard to hit. When someone is hitting like five keys or more a second, rearranging the keyboard is probably not going to make a big difference.
Engineers: failing at real-world thinking since...well, forever.