Amazon chooses shipping defaults to benefit themselves.

With prime I have to manually select the shipping speed to get it the fastest.

Without prime, it defaults to faster shipping that you pay for. You have to manually select slower shipping to get the advertised "free super-saver shipping"

For me, most products get delivered in 6 days with Prime. It has stopped making sense to pay for the Prime subscription. It's cheaper to pay for faster shipping, given that I only order 1-2 items monthly.

One nice part of shopping on eBay is their proximity sort. IME this tends to minimize shipping time (and, of course, carbon footprint). When I order something locally from the LA area, it’s usually there the next day or two even with free shipping.