If I had to guess, and it will sound difficult to accept, it's probably this:

Amazon expects you to ship them inventory weekly to avoid over storage. By sending them product once a month or every other month means they will have high inventory and space usage when it first arrives and that space is slowly restored as your product sells. If you sent them 1000 units and it takes three months to sell 1000 units for example, their argument is why not send 100-150 units weekly to cover weekly demand. It's more work on you as a seller and better inventory management and less resources for them to use. The feature offer kinda resets weekly so I can see why that might be what metrics they're looking at. I talked to a book vendor at a trade show and they literally had POs from Amazon that show 200 books week 1, 250 week 2, 300 week 3, "return" 200 week 4, order 150 week 5. The amount of storage space used is important to them.

Amazon FBA isn't a "warehousing" solution but a "fulfillment" solution. They make money picking and packing your orders, not storing it. They want products that sell fast so they can make their cut of each sale and sellers needs to be able to realize the difference between selling something once a week and selling it once an hour on Amazon. What Amazon wants isn't what we as sellers want at times and we as sellers need to figure out what they are willing to do for us and not what we demand of them.

AWD seems to be Amazon's "warehousing" solution. And yes, they probably want FBA sellers to use AWD for long term storage solution where goods are stored in bulk outside of high volume/traffic areas of the warehouse where goods are constantly being moved in and out such as them having goods in an FBA facility in California and Arizona to serve West Coast sellers but also the bulk of it in an AWD warehouse in Texas to supply those FBA centers as they need but the warehouse rent for long term in Texas rent is much much cheaper and distribution to other states easier. Amazon decides how often and when to send goods to the FBA facility. Plus it's also easier for them to decide 5% goes to FBA 1, 10% goes to this FBA 2, 7% goes to this FBA 3 rather than splitting it up in the beginning and as one facility runs out transfer from an FBA 1 2 & 3 to an FBA 1 2 & 3. There is now a central AWD hub that supplies X amount of FBA 1 2 & 3 and the central AWD hubs transfer larger shipments to each other creating less smaller shipments. AWD is likely going to be used by big brands as a way for Amazon to warehouse goods from Nike, Kellogg etc so it's only going to get bigger.