This trend is not just in retailers. I have clients asking us who _our_ vendors are, and if _they_ are on AWS, and trying to push us to vendors not using AWS.
But I don't understand why they'd care. I can run websites on any cloud.
Because Amazon uses the profits from AWS to keep running their retail business at a loss and suffocate all competition in that space. It's not hard to understand why retail companies don't want to spend cash on their own destruction.
Probably logistics companies, electronics, companies, and quite a few other industries that Amazon is trying to compete with.
Because if you can run websites on any cloud, then they don't want you to run them on the one that funds their rival's expansion.
This is true for every major cloud provider. Certain industries are unwilling to use certain clouds because it is funding their competitors.