Amazon is much worse on shipping than pretty much any other online retailer. The norm is that the retailer tells you when the thing will arrive, and it arrives on time. The norm for Amazon is that they advertise a deadline they don't plan to meet, and when they slip that deadline, they alter the shipping speed displayed on your order.

A long time ago I assumed that Amazon removed shipping speed options from their ordering process because, if you itemize shipping separately from the cost of the good, the customer can demand a refund on shipping when you don't provide what you sold.

My current theory is that it's a side effect of deciding they needed to provide shipping in-house instead of buying it from reliable sources. They replaced shipping they could control with shipping they couldn't control, and so they stopped letting you specify the shipping speed you needed. But for some reason they continued advertising shipping speeds they knew they couldn't provide.