If Google can measure how many people they lose by a millisecond of added time between a question and a response ( https://www.forbes.com/sites/rogerdooley/2012/12/04/fast-sit... )...

Then there has to be some sort of measurement out there on how each step causes cart abandonment (or whatever it's called).

Its the same reason sites add Single-Sign-On... click click, I'm on a website... vs filling out forms, verification, etc...

Yes, but adding 1-click also inserts an extra semi-step into every purchase: the choice of whether to click the 1-click button or the add to cart button.

Apparently Amazon finds that adding 1-click does more good than harm.