The reason why Amazon reduced their vendor program is because they were getting scammed. Here's an example:
Vendor sells Amazon 500 shirts at $4/unit, retails at $10.
Once in stock, vendor sells the shirts very quickly. They do this by either putting the shirt on sale for pennies, or by using hacked accounts to buy the shirts (or by paying people to buy the shirts).
What happens when Amazon sees that the shirts they ordered sold out in 3 days, and are going to take 30 days to replenish?
They buy more, and although the vendor may have initially been down the $4 * 500, when Amazon places that reorder for 5,000+ units, the vendor is up substantially and bails, leaving Amazon with a ton of inventory.