For me it’s the fast shipping I can’t live without.
I recently moved into a new apartment and needed to run a network cord from our router to the other side of the apartment to put an access point so we’d have good WiFi coverage. I went online to several other retailers for the few things I needed (cat6, crimp tool, and a few other things), but all of them wanted me to pay ~$25 or more for their slowest shipping option of 5-7 business days.
Meanwhile, Amazon had everything at my door the next day with free shipping. I tried to avoid Bezos, but I couldn’t. :(