It's a mixture of people upset that they didn't get the weapon skins for their guns because they didn't preorder and people who let the hype lead them instead of making sure the game would have what they want.

A good example is NMS. Very little was actually shown other than the basic crafting and exploration. People let themselves be worked up into a frenzy that there was going to be more than that instead of taking it at face value that it was going to be a crafting and exploration game.