[dragonwriter]

Since they are set open, I assume they are actually using them as if they were en-dashes and not em-dashes, which the more common style would be to set closed, but I’m guessing, in either case, the reason is “because you can type it on a normal keyboard without any special modification, Compose-key solution, or other processing, and the author doesn't care much about typography”.

EDIT: Though these the days it could also be an attempt at highly-visible “AI didn't write this” virtue signaling, too.