My guess is monopoly (approximately). ISP choice for the vast majority of US people is practically nil - you either have a cable provider (Comcast, Cox, Spectrum, etc.) or a phone provider (Verizon, AT&T). With priority shipping, if you don't like Amazon's non-subtle nudges to you to pay for Prime, you just move on to Walmart.com, Rakuten, or an eBay vendor. Treating ISP as a utility company was the right model and the current FCC is not doing consumers a service by killing this model.