At least in terms of the Bolex reflex models, the image is quite dim, so a tight fit for the eye is needed. Making eyeglass wearing not practical. Many, many still cameras work fine with eyeglasses. Therefore not as much need for a corrected eyepiece.
Some exceptions in my work:
Rollei 3003/2000F cameras work better with the eye close to the finder; like a movie camera. Therefore have an adjustable eyepiece.
Bessa R4 (21mm finder) only useful for 21mm if the eye is close to the finder. It is not adjustable, but takes common Nikkor diopters.
I'm sure there are many other still cameras that function poorly with eyeglasses.