I've been left-eyed until recent years, when a cataract was growing worse in that eye. It got so blurry I switched to the right which had had cararact surgury a couple years earlier. It seems a matter of habit for me; now that I've developed the habit of raising the camera to the right eye I still do so even though the left eye has good vision now too.
Remembering back to my getting more serious about photograpy years ago I recall experimenting with how best to hold the camera for vertical orientation shots. Because of being left-eyed I got a better "connection" to the viewfinder when the camera was held right-side down. Also I though holding my right arm way high for right-side high holding would draw more attention to myself. And, particularly with RF cameras, holding right-side low makes it easier for the left hand to stay clear of the viewfinder window while moving the focus and aperture settings. Finally, I think right-side down promotes a steadier hold, as both elbows can be pressed agaist one's sides. So it all worked out, and it's not so different right-eyed except for attempting a good view for verticals.
Now I seldom use my left eye for the viewfinder, depending on circumstances. For vertical shots with the Pentax 645 though, the configuration of the camera grip is less convenient right-side low. So for that I prefer the left eye since the camera has only a small ring eyecup that pokes me in the right eye by getting too close too easily, and using the left eye the camera body is steadied better by my forehead. But I may switch to right-side down with this camera too, using my thumb on the shutter release...