'Everything' can stand alone. It replaces a noun. 'All' doesn't usually stand alone. It qualifies a noun. For example, you can say: 'He was so hungry that he ate everything in the fridge.' ('todo') or 'He was so hungry that he ate all the food in the fridge'. ('toda la comida' )

You should look for real examples (sentences) instead of some clever rule. "All" is typically an adjective or adverb. It's possible (but not common) to use it as a noun or pronoun. "Everything" is a pronoun.