Huge chunks of metal could be safely removed from some of those.
Then why didn't they do that?
Increased production cost (more machining operations), but the real factor is that the excess material is so close to the shaft center that the inertia reduction is really small.

I would like to see an FEA though. The diagrams are easy to interpret, the industry has settled on "red = bad, yellow = needs work, blue = good to go". The ideal rocker is really thin in surprising places, taller than you might guess, and shows nothing but blue all over. The "art" part is how you stress the rocker, and how much, intuition helps you figure what it might do wrong (and is therefore stressed out of its plane of strength).