Along with many other horrible anticompetitive and illegal activities (and a few amazing positve things), Amazon's free shipping isn't free. Somebody is paying for it, and if you think it is Amazon I have a bridge to sell you.

People with far more expertise than I have broken down how "free shipping" for online purchases that Amazon has led the way on if not pioneered, is just another hidden cost in your purchase on Amazon. Lots of videos and papers on this subject.

The old saying, "there ain't no free lunch" always applies to businesses.