I think "why" is a reasonable question. The speedometer is much more visible in my car. If I were racing, I'd probably be more interested in RPMs than MPHs, and having the tach on the right would be preferable. I do not race, so having the speedometer on the right is preferable (to me).
I am also driving a Ford F150, a Ford Expedition, and a Mercedes 230SL. All of them have the speedometer on the right and, no, I have not moved them there. In fact, I do not recall having a car with the tach on the right. I suppose the 1971 240Z did, but that was over 40 years ago, and I don't remember that detail.
It would be a considerable disappointment to remove the dash only to find the gauges cannot be switched, so I guess I'll forget about it. Perhaps someone who has switched them will chime in and persuade me it is reasonably doable.
Thanks for the input.