Amazon's backend sales systems and seo are so deep that we couldn't possibly understand what happens under the hood. What I can guess is that their systems work purely off numbers and availability. Their systems most likely adapt on the fly and it optimizes results as it goes.

No tbev in stock? Must be gone. tbev in stock and #1? Let's add to the top of the list.

It's all automated. I doubt they really have full control of how their systems work through inventory.