Amazon has competitors, a central government do not. If the central planning fails to deliver a product then there is nobody there to deliver the product, if that product was food then people starve. This lack of competition is both bad for robustness as I described, and bad for efficiency since it means that people has to get their goods from the government and can't choose to get it somewhere else, so there is no selective pressure to keep the government deliver goods people want. You could say that other countries pressured them via war, but the people couldn't choose to buy American, the competition happened at a way too high level to matter.

Or rather, ultimately the people made their choice, central planning was scrapped and people could but American goods. So in a way the competition helped, people ultimately picked the superior option and the inferior option went under. But it took a very long time for that to happen, capitalism is way faster.