This usually comes from a couple things.

• The Amazon site that could do faster delivery was out of stock, had too many orders already to deliver it same day on Wednesday

• The time of day you looked at the order changed so you got in on Thursday early enough to hit that time limit

Or the Most likely:

• When you were placing the order it checked the available shipping methods (not days) and they couldn’t do same say that day, so they offered standard. The next day they check the methods again (probably taking into account the above reasons) and they could do same day so they offered it.

They don’t do the “what about same day, but tomorrow” stuff because it’s usually a problem that solves itself. Either you’re fine with Saturday, or you come back tomorrow trying to get it same day again.

The thing that is worth noting is that Amazon doesn’t do everything they sell as fast as humanly possible. They still have logistics to worry about and not every possible site can ship everything at maximum possible speed. They probably could if they forced it, but the juice isn’t worth the squeeze on that approach.