Click on the word "Here"s" for the article.
There have been a few made, but during the hey day of SXS rifles SXS shotguns also ruled. It made sense for rifles to be configured that way because of the familiarity with shotguns. O/U shotguns are much newer and by the time they were popular most African big game hunters had moved on to bolt guns.
Even with shotguns many shooters still prefer the handling qualities of a SXS over an O/U for fast quick shots. I know I do. O/U shotguns are favored for competition, but less so for hunting.
And as the article discusses, a SXS requires less movement to reload than an O/U making it faster to reload quickly. While I've never used a SXS rifle I have used SXS and O/U shotguns. This is a real thing for me. It's not just that you have to open the action wider on a O/U, but it is a lot slower to get the shell/cartridge in the lower barrel. But not everyone agrees with that point.