The internet is packed with Software Development Kits (SDKs) and Software As A Service products (Saas) aimed at optimizing your social and user experience.
SDKs such as UXCam, record your screen every time you’re using a certain app, so to check on your experience with such an App. SaaS products like Hotjar are monitoring user sessions on website so to check on the most active portions of any page, checking your IP address, device ID, GPS location and email. Your interests, demographics, preferences and purchases are then going to be share with all of the apps using the same SDK or SaaS, so that everyone knows how to tweak your experience.
Countless startups buy and sell lists of information to companies. That’s how you always seem to be getting the ads you were looking for online.
Before you freak out, all the information are obviously anonymous, plus you have to remember that as much as it is a pretty intrusive technique, it is also what makes your internet experience enjoyable and custom-built.