Please remember that all answers in /r/AskHistorians must be based on in-depth historical knowledge. We've already had a few comments repeating that QWERTY was deliberately designed to slow down typing and avoid jams – an urban legend. If you didn't already know that, you probably shouldn't be answering this question!

Was it simply a matter of being first on the field

While QWERTY, during its invention, wasn't the only keyboard layout that was around, gradually consumers made the choice to use it over the others. QWERTY keyboards winning various typing competitions helped persuade the masses. Which meant that over time, the keyboard became the standard.

So by the time Dvorak came along, QWERTY was the conventional and ubiquitous choice. Which meant that Dvorak would not only be compared to QWERTY by consumers, but consumers would have to be convinced that it was superior enough to abandon QWERTY and make the switch. Basically, Dvorak had to dislodge the standard...which is a big ask for a new item.

Which then laid in the heart of why Dvorak was never really taken up - there isn't a big advantage in using Dvorak over QWERTY. A lot of the initial claims about the efficiency of Dvorak were either by the inventor himself, or were drawn from the results of flawed studies. Many later studies have found there isn't a significant advantage in either speed or ergonomics regarding Dvorak.

If you add that you'd have to retrain yourself to use Dvorak after learning how to type using the standard [QWERTY]...then there's no real major incentive to switch. So Dvorak remained a minority keyboard layout, and QWERTY is still the standard, even to this day.

An interesting article about this, although old: The Fable Of The Keys