Hello, There's probably a story that goes with it.
1) The female end was probably part of an extension cord. I say this because it appears to be of the molded type. Perhaps the extension cord was damaged and that end became available.
2) The 5 or 6 inch length might provide some advantage from the drape off the outlet; perhaps even a place to tie off.
3) Since a common ground lift (3 to 2 adaptor) would've done the same job for 75 cents, it's likely the assembler didn't pay for the male plug unless he needed to. Perhaps an adaptor with something plugged into it was too long and fell out of the outlet.
What do you think of this Watson? Kira