None of that requires a conspiracy. I’m working with a client here in DFW that is attempting to get a series of new exercise devices to market. Amazon has made themselves a supremely attractive distribution partner by making the extent of our customer side delivery interactions be “send it to Amazon and let them deal with it” - *for less than the cost of the company warehousing, packing and shipping it ourselves, Amazon does that for us.* We don’t even have to have a company warehouse, the contract manufacturer drop ships it to Amazon on our behalf. If Amazon decides to carry the item themselves instead of just being the fulfillment system and marketplace we sell through, they even deal with all the customer service for that item, reducing our costs.
No other distributor/reseller has anything nearly that attractive. Walmart’s Marketplace is a nightmare, selling *to* Walmart itself is even worse. Jet is trying but they’re still not good, etc. So we end up sending product to Amazon and if someone else wants the product in large quantities without Amazon being involved... well, we’d have to set up special measures and actually charge more.
When Amazon is making itself that attractive to work with and reducing costs that much on the seller’s end... yeah, it doesn’t take much to see why Amazon has the supply it does. No conspiracy needed.
A problem is that Amazon watches what fulfillment items sell well and when they start buying and selling the items directly, the original "partner" loses the customer base he built to Amazon direct.