Bacteria

My understanding is that the Red Wriggler worms, also known by their formal name “Eisenia fetida” don't eat the food scraps – that bacteria break down the food scraps and that the worms eat the bacteria.

My understanding is that the Red Wrigglers don’t have teeth; that the common garden worm (the one you see stranded on the footpath after a rain storm) does have teeth, and can chew on the leaves it drags down into its burrow.

Once you think about it, if the bacteria can't break down your food scraps, then the worms can't help at all.

Consider foam plastic trays: bacteria don't eat polystyrene foam, so the worms don't get to help get rid of the polystyrene foam trays.

Consider apple cores: bacteria do break down apple cores, so worms can help.

Think "bacteria", it will explain a great deal.