See I didn't grow up thinking I was using commas to separate list items, I grew up thinking I was contracting a bunch "and"s. That is:

  A red one and a blue one and a green one and a purple one.
  became
  A red one, a blue one, a green one and a purple one.

Notably kids seem to do the first one naturally.

If commas were list separators and not just a short hand why would we end them with "and" at all.