1. Is Google really all in on product search? Their product search is pretty bad at the moment and it's a very challenging search space, esp when you work with tens of thousands of retailers. Going directly to retailer/niche-platform sites usually works better for me. For example, for music related I go to reverb.com, for outdoor to rei.com, etc. I then to Google and Amazon for reviews if needed.
2. Distribution and fast shipping is something Amazon has invested in for decades. I still need to wait longer than a week to receive items from retailers such as REI and others. Not an easy problem to solve.
3. Competing with Prime. Amazon ships everything including groceries. That's a big plus of Prime. Not only you get fast shipment, but you get everything you may need so you rarely need to use a different service. And with a credit card from Amazon you get 5% cash back on purchases. Everything is included.
Disclaimer. I own Amazon stock.