That's exactly what I'm saying. We forget that it wasn't so long ago, only a few years back, when we had displays that were actually much smaller than the outer Fold displays as the norm. But, as you say, even today many phones are about the same width or even smaller.
The thing is, the Fold series had to take usability into the equation. If the outer screen were as large as say a pro max iPhone, then when opened it would be huge and difficult to hold with one hand (yes I do that on occasion if I don't need to navigate much), or even 2 hands as it would be that much heavier as well as wider. I'm curious to actually hold and use the Mate 2 as it is wider and they have that narrowing design to accommodate for the weight distribution, but at the end of the day I suspect it's still heavier and side heavy when used unfolded.