I have noticed for the last 6 months or so, at least here in Phoenix, that Amazon frequently does not deliver items when they promise. It is not just an issue with the shipper, in the last two cases the item did not even ship until 1-2 days after the date they promised for delivery.
This has reached a head in the last week, when I ordered a number of items to be delivered immediately -- I am leaving town and wanted some items to take to my son's apartment. They are useless to me even a few hours after I depart home. I ordered seven items on Monday with my prime membership, and all promised delivery that same day (one for free, two with a nominal upcharge). Of these, none arrived on Monday. One arrived on Tuesday and as of 4PM on Tuesday, the other six have not even shipped, and Amazon is showing them here on Wednesday at best.
I would not have bought these from Amazon had they given me accurate delivery estimates. I am wondering if they are using fake, overly optimistic delivery estimates to try to woo business from bricks and mortar stores, whose one advantage is immediate fulfillment.