Here's why:
* Common nouns refer to general, non-specific things.
* Proper nouns refer to specific people, places, or things (e.g., John, London, the Eiffel Tower).
"Wax" refers to a general substance, not a specific type of wax. We use it to talk about wax in general:
* "The candle is made of wax."
* "Bees produce wax."
Let me know if you have any other questions!