Ask HN: Why is the Amazon purchase experience so hilariously bad sometimes?

On Tuesday I bought a book. Amazon was selling it with two-day shipping for Prime members. Cut to today, it's not projected to arrive until Monday. More than slightly late for something that should have only taken two days. Oh well - lots of Prime members have similar experiences. But this next one takes the cake for me. On Wednesday, I buy an electric toothbrush. I place the order at 11:00 am. At checkout, they tell me they can get it to me same day, between 2:00 - 6:00 pm. Err, seems slightly ambitious, but it's free, so why not? Predictably, the toothbrush doesn't arrive same day. Nor the following day. And now when I click Track Package, they tell me that it's likely lost, and maybe I want to request a refund. So I request a refund and they tell me that it will take 3 - 5 days to process, and also that I'm obligated to return the package if it arrives in the interim. So now I'm stuck trying to decide whether to re-order through Amazon or to go with a different website, plus I need to find time to go to the Amazon store due to their screw-up. And further, there seems to be no way to complain to Amazon about this. It used to be that if they missed their delivery targets they would credit you with a free month of Prime. That no longer seems to be the case, as far as I can tell. The part that is so frustrating though is that in the back of my mind I knew that there was almost zero chance that the package would be delivered same day and that I would be better off doing a different shipping method. I don't understand why they would go out of their way to set users up for such a bad experience.