I m well aware that they make that discount. However, I assume the discount comes out of Amazon's pocket, just like the other retailer eats the cost.
That is what a wholesale model
does. It lets the retailer set competitive prices based on what other retailers offer.
I assume, without hard evidence, that Amazon demands the most favorable terms
that the supplier offers to other vendors. Because with a wholesale model (where this is relevant) the retailer prices literally have nothing to do with anything whatsoever.
Dur.

I mentioned Agency to demonstrate the obvious difference between the two. Use your deductive reasoning skills.
If anyone has some sort of evidence or any reason whatsoever to think Amazon makes suppliers eat the cost of Amazon price-matching a cost that Kobo/Google/B&N eats, please lay your facts on the table.