They do pay you ... in kind. They built a way to share photos, send messages, etc etc

I thought that was the end game originally - reward users with cash for self providing information companies usually need to pay survey companies to get.

Why pay users when they give it to you for free?

Why does Facebook spend money on employees then?

Presumably Facebook employees would work else where if they weren't paid.

My point was that what people aren't giving their info to Facebook for free, Facebook has to spend money on their employees to create something which people then want to use resulting in them getting information.