https://www.costco.com/Post-Honey-Bunches-of-Oats-with-Almon...
https://smile.amazon.com/Honey-Bunches-Oats-Almonds-14-5-Oun...
https://www.costco.com/Post-Honey-Bunches-of-Oats-with-Almon...
https://smile.amazon.com/Honey-Bunches-Oats-Almonds-14-5-Oun...
https://www.amazon.com/gp/product/B00IAE91AI/ref=afx_dp_ingr...
I feel like that's pretty revisionist. For a very long time, shopping at Amazon was about price first, variety a close second, and convenience a very distant third. I doubt so many people would have developed a habit of shopping there so much if the advantages were truly "convenience and variety" first.
Amazon's prices have gotten much less competitive the last several years, which has disrupted the value proposition that caused many people to choose it.
I find it hard to believe that free 2 day shipping and free customer-first returns did not sway opinions though since it basically pushed the entire industry forward.