One word: ergonomics.
With Dvorak, the most commonly-used letters are on the home row. In fact, all of the vowels are on the home row.
The most common letter in English is E, and QWERTY makes you reach for it. You know what IS on the home row? Fuckin’ semicolon! Can you even remember the last time you used a semicolon?
I spend a lot of time at work sitting, so I’d rather have a comfortable chair than an uncomfortable chair. Same with my keyboard: I’d rather have a comfortable layout than an uncomfortable one. Less risk of repetitive strain injury, too.
https://www.youtube.com/watch?v=188fipF-i5I
This video goes over a lot of metrics about how far you have to move your fingers to type certain things, and how we wound up at qwerty in the first place. The truth of it is though: different layouts are better for different things. He shows in the video a bunch of keyboard layouts optimized for things like youtube comments, the script of the Bee movie, wikipedia, etc.
At 7:12 in the video, he cites Dvorak as 26.2% more efficient than qwerty for how much your fingers need to travel to type. This covers letter frequency, but also sequencing (ie, typing the letters “un” on qwerty means i have go from top row U to bottom row N with the same finger).
I don’t use dvorak, because if I want to use someone else’s computer, I don’t want to have to fight with muscle memory, but it is “superior” in many ways.