Why Facebook, Google, and Amazon Track us?

With the advent of apps by Google, Facebook and Amazon, every other Smartphone user is amazed with the news that spread like a fire worldwide in spite of looking for the loopholes hidden behind the screen.
As many apps can't work without demographic location, the same case applies with these giant search engine, shopping as well as social media app, They keep tracking the users to find essential details what they actually do as well as their likes and dislikes. Upon collecting data, they display advertisements as per the data stored by them. Facebook, Amazon and Google track feature is encapsulated with coding that store each and every activity of yours and start displaying ads whenever you rush to any online store.