When you load a webpage or an app that's hosted on AWS you give Amazon a lot of information about your browser, location, etc. They could very easily aggregate all of the AWS services you load things from to build a very detailed profile about you. If Amazon were being nefarious they could inspect the data in the packets you send across their network.

Using a site that's hosted on AWS === doing business with Amazon. It's just a very one-sided relationship where they get a ton of useful data and you get to load a JS app.