Notice, no CA cities
This is because Amazon doesn't want to have to pay sales tax in California. Which they would have to do if they had a "substantial presence" here. As soon as they open a distribution center in Cali to provide this service, they have to start collecting the 9.25% sales tax from California customers for all on-line transactions. It ain't gonna happen.
Frequently I can get stuff from Amazon far cheaper than in retail stores here, because the lack of sales tax (at nearly 10%) trumps a higher cost of the item, even when I have to pay shipping costs.