Social media platforms — Instagram, TikTok, Facebook, X, YouTube — are free to use. Building and running them costs billions of pounds. The gap between "free to use" and "costs billions" is bridged by one thing: advertising. And to sell advertising, the platform needs to know as much as possible about you, so it can target ads with extraordinary precision.
The business model
You are not the customer — you are the product. Advertisers are the customers. They pay the platform to show their adverts to specific groups of people: "show this ad to 25–35 year olds in Manchester who are interested in running and have been searching for trainers." The more the platform knows about you, the more it can charge advertisers for that precise targeting. So the platform's core interest is in learning as much about you as possible and keeping you on the app for as long as possible.
It's like a shopping centre that's completely free to enter and full of interesting entertainment. You never need to buy anything. But every shop you browse, every product you look at, every conversation you have with friends inside the centre is recorded. The centre then sells that information to advertisers: "this person looked at three trainers shops, two coffee shops, and lingered near the book store." The entertainment and free entry are the bait. Your attention and data are what's being sold.
Why are feeds designed the way they are?
The infinite scroll, the notification badge, the "like" button, the auto-playing next video — these are not accidents. They're carefully engineered to maximise time spent on the platform (called "engagement"). Variable rewards (sometimes your post gets lots of likes, sometimes none — the unpredictability is deliberately addictive, the same mechanism as a slot machine) keep you checking back. Outrage and strong emotion drive more engagement than neutral content, which is why inflammatory content tends to spread further.
What about your data?
Platforms collect far more than what you post. They track what you look at (not just what you like), how long you hover over each post, what you type and then delete, your location, what other apps are on your phone, and connections between your behaviour and hundreds of third-party data sources. The detailed profile this creates is used for ad targeting and sold to data brokers. GDPR regulations in the UK and EU give you rights over this data — including the right to see what's held and to request deletion.