I don't see the 2 larger legs doing all that much creeping, the creator simply didn't design them for creeping.
Next time you see a grasshopper in the wild, watch and see just how much those jumping legs are used in creeping.
Tom! We don't have to wait to see one in the wild when we can watch it on-line:
Grasshopper "creeping" movie courtesy of Texas A&M.
Gee. It sure looks like those two "jumping" legs are doing a heck of a lot during "creeping". If the creator didn't design them for creeping, then why are they used during creeping?