[blablablerg]

Only a small percentage of people are willing to pay for internet services. It is psychology and competition between the sites who offer services for free vs requiring payment. Paying for a service is a barrier to entry, while getting it for free and selling your data instead is not perceived as such. That is why all the big sites never would've taken off if they had paywalls.

[viraptor]

That and regional differences. The amount that people in many regions would be able (not even willing) to pay would be tiny for the company running the site in many cases.