Kodshim was prohibited because of Golden Calf

 Mechilta (Yisro  Bachodesh 2) From "a kingdom of Cohanim" it is derived that all of Israel were fit to eat of the offerings — until they made the golden calf. Once they made the golden calf, the status of Cohanim was taken from them and given to the official Cohanim, as it is written  "A scattered sheep is Israel, harried by lions … first it was devoured by Nevuchadnezzar, king of Bavel, etc." It (Israel) is compared to a sheep. Just as a sheep, when one of its lambs is smitten, all of its lambs feel it, so, Israel, if one of them is smitten, all of them feel it. As opposed to the nations of the world. If one of them is killed, all of them rejoice in his downfall.