Can someone explain how we arrived at the pelican test? Was there some actual theory behind why it's difficult to produce? Or did someone just think it up, discover it was consistently difficult, and now we just all know it's a good test?

They are not good, and they seem to get worse as you increased effort. Weird

None of them have the pelican's feet placed properly on the pedals -- or the pedals are misrepresented. Cool art style but not physically accurate.

https://pelicans.borg.games/

I tried getting it to generate openscad models, which seems much harder. Not had much joy yet with results.