???
The reason for looking for tires with taller sidewalls is for increased impact protection. I have literally 3 miles of bad dirt road to traverse every day. The GL1800 tires are significantly taller in this regard - "falling off the bike" is not generally a tire sidewall issue...
While Honda went with larger diameter wheels, they subsequently switched to tires that were "shorter", pretty much maintaining the same ride height. Almost like they were trying to follow the current "big wheel/small tire" look so loved by our local custom car scene...
It would appear to me that aesthetics trumped usability... Have a friend who runs a wheel repair business in town. He LOVES these things (big wheels/small tires)! Every time I go to see him he has a few wheels in the lobby waiting for repair - because someone took a 1" height driveway entrance too fast and there was not enough sidewall flexure.
I have a rear GL1800 wheel/tire that I may try to fit just for grins - they are all (GL1800, F6B, F6C) supposed to fit the same swingarm - there are also a couple different sizes available, with over an inch diameter difference. Fronts may be a different story, as the forks vary considerably...