That is actually not the case for PRIME NOW; you are thinking of
Amazon Fresh. PRIME NOW has a ridiculous amount of items in a simple to shop store with pictures. You can either narrow the store you want to shop from or shop from all of the available retailers in that particular locale. They are bringing on more vendors it seems as it builds speed.
For example, yesterday I ordered groceries from PCC, my local natural co-op market that is the bougie organic brands and then a separate order came from Amazon's facilities of all the regular stuff like breakfast cereal, TP, etc. You don't have to choose a market to begin shopping, just search and it will show which retailers have it and the price. (in my area its PCC, Uwajimaya, New Seasons, All the Best Pet Care, & Amazon) There is a $30 minimum per retailer. You just shop and the cart separates for you. You check out one by one but it costs you nothing more to have a delivery from one store or three. Typically the store is preparing it for the driver so you don't get all the texts from the shopper and questions and substitutions. If an item is out you will get a text but many times the preparer will text if you would like to substitute. Rarely happens. It is by far a superior situation. Instacart took me as much time to deal with the shopper as it did to have gone.
Prime Now is not available in most areas yet. But it IS available in Orlando & Anaheim. AND in metro areas, there is restaurant delivery too. Anaheim has it, not sure about Orlando.