It's not deep scanning your hard drive to try and figure out your SSN or medical history like some people think.
But people pick AWS because it offers a lot more than just a storage bucket. Same with Google Analytics. It offers a ton of ecommerce analytics including custom tags that can be set by the shop owner. TeeSpring is probably not a full-service Ecomm platform like Magento. It's likely that they are piggybacking on GA's built in Ecomm tracking and reporting capabilities, instead of reinventing the wheel by doing it themselves.
FYI, Ublock Origin also blocks links to "sponsored results" shown on Amazon search.