It's economics 101 - the price you pay for something is derived from the supply and demand curve (ideally.) Artificially altering or limiting one of these will disrupt the other values. If you set your price to zero, then demand becomes basically unlimited. So now you have unlimited demand, limited supply (your servers can only handle so much traffic at a time), and no income to pay for it. Imagine if McDonald's announced tomorrow that hamburgers are now free to anyone who asks for one - the lines would be out the door and they'd loose millions of dollars. So Facebook (and others) adopted the broadcast model - provide the service at no charge and instead collect revenue from your *real* customers; advertisers.
But that model is inappropriate; it works for TV and radio because the costs to create and broadcast your content to 10 people is the same as, say, 100,000 people (in the same geographic area natch.) So the more people that tune in, the more money you make by being able to charge advertisers more for more eyeballs. But for Facebook et al., the cost to serve cat photos to 100,000 people is potentially (I have no idea what the real scalability values are) 10,000 times more than just 10 people. So the more people you add, the more money *per person* you have to extract in order to become/stay profitable. People will reject a site if it has too high an ad to content ratio, so an easy way to increase the number of ad views (and therefore revenue) each user generates is to get them to keep loading new pages. And since people seem to dislike the idea that knowledge is being kept from them - especially when the only perceived cost is the click of a mouse button - News SPAM is born. Another way to go is targeted advertising, which also arises from this misapplication of the broadcast model. Unlike News SPAM, targeted advertising requires real additional effort (read: costs) to implement so Click Bait flourishes.
It would be very interesting to see a breakdown of the costs and revenues that each Facebook user represents. I don't think people would like being shown that information, but maybe I'm wrong?
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