Am I insane? Surely single-piece hoods are possible.

So I've been researching making a hooded poncho, and every tutorial/pattern I've seen suggests making the hood out of two pieces, sewn together so the seam runs up the center of the hood, perpendicular to the front edge. Further research into making other hoods has revealed the same thing.

It's highly likely that I just don't know how fabric works but - couldn't you acheive something almost identical with just a single cut of fabric? Something like this: https://i.imgur.com/VDhGxs8.png
with the dotted red edge sewn along the back half of the neckhole in the main garment? It seems like the shape might fit slightly differently on the head, but I genuinely can't figure out what's wrong with this.

I'm happy to be wrong, but it's slightly driving me insane that I can't figure out why X_X