That interesting. I've noticed that Amazon always takes longer to load and spend more time at a poor bitrate, while Netflix just works.

Netflix beats others when it comes to low bitrate high quality streams. At some remote areas with poor cellular coverage, Netflix is the only service that provides a working video stream.

So it only solves a tail problem. I would assume the percentage of subscribers with poor internet is low.

Why would you assume that?

It also helps Netflix. Lower bitrate means less server load and lower internet bills.