Addon items not existing

In some addons, most addons, allmost all items that aren’t spawn egg’s don’t exist, they don’t appear in any inventory or command giving. There are a few items besides spawn eggs that are exception to this, though it is unknown why. This is really annoying has it completely ruins the modded/addon experience. Addons are mainly immune to this, though this is still a pressing issue. It may effect other versions, but it was created with this update.