Oh, okay. I thought it would be something more esoteric. Youtuber About Here has done a few videos mentioning the two-stairway rule, but he explains it as being

Oh, okay. I thought it would be something more esoteric. Youtuber About Here has done a few videos mentioning the two-stairway rule, but he explains it as being mostly a barrier to multi-story multi-family buildings being built on SFH-sized lots. In any case, he posits that fire mitigation strategies developed since the code came into effect (mandated sprinkler systems, fire breaks, etc.) make it unnecessary. There's also the notion that fire escape infrastructure doesn't need to be a whole other stairwell. It's one thing I hope to see change in the future.