Or a signal that Amazon has reached the required level of incumbency that it doesn't need to worry about speed any more.
I see hundreds of tweets by @amazon that reply to people complaining how deliveries miss the dates that amazon dot com promised but then amazon dot com probably delivers so many packages every day that I think it is a bit of column A and a bit of column B here.
To the contrary. At least in my area, there are more items with 1-day shipping than ever before.
A few years ago, most stuff was 2-day. Now most stuff is 1-day. And it's constantly popping up options for same-day too.
Or also signal that they've learnt about exactly how many of us stopped using Amazon because we got tired of receiving counterfeit products because of the commingling...