I have looked at and handled a couple of Wranglers and liked what I saw. Not so much with the RR's I have handled. A wrangler might be in my future if I didn't have a couple of single sixes now. And the fact that it doesn't have a 22 mag cylinder is sort of a deal killer.
I don't think that there is much doubt that they are a better firearm. But. like you say, some shooters do want the combo option along with adjustable sights and maybe a 6 1/2" or 7 1/2" barrel length for greater sight radius and accuracy. I can't see much point in shooting a .22 magnum SA revolver frequently otherwise, considering the ammo cost.
On the other hand, some people just end up buying a combo .22 revolver (like me) because it's available with the options that they want, and they can inspect it first at their LGS before they buy. They don't need or particularly want the .22 magnum cylinder, but it comes with the gun that they want. Also, with Ruger at least, the solo-cylinder .22 Single Six choices are limited, so you end up having to buy the combo.
That isn't a negative really, because the price difference often isn't that much, and that spare cylinder is desired by others if you end up selling the revolver later. But, many will buy the gun, shoot 50 rounds of .22 magnum out of it just for the heck of it, and then clean and store the spare cylinder safely away, never to be used by them again.
Anyway, I guess that Ruger is selling so many Wranglers right now that they don't see any need to offer more barrel and sight options, or a combo gun. Or, maybe they just don't want to compete against themselves with the Single Six.