it's crazy because I've seen "implement flappy bird on an FPGA with VGA output" as a 2 week project to a human as something immediately understandable.

Maybe it's the smoothness of motion that makes these games understandable and LLMs seem to consistently fail at that. Ask them to do something snowboarding and they go really hard on the physics since it seems like they don't know what kind of approxmations feel good.