Why am I being asked to submit approval for a brand that already exists?

So let’s call this brand “XYZ”, it already exists in the Amazon marketplace and I can typically piggyback off any existing listing with that brand. However I’ve come across a few products from the same brand that aren’t listed on Amazon. Why is Amazon asking me to submit for approval for an existing brand when they turn around and let me sell the already existing brand that are already on the site? I can understand if the brand doesn’t exist but it does!