[falcolas]

Then why would you ever put it on a website that generates its revenue from using and selling your data?

[nathanaldensr]

Because you're (not you, but people in general) are dumb and overly trusting.

[marlowe221]

This is the correct answer.

[blantonl]

Because you agreed to do so under the terms of conditions of that website.

[nlh]

Look I understand you point from a legal standpoint, but do you really truly believe even a small fraction of FB and IG users actually “agreed to do so under the terms and conditions of that website”? They just clicked whatever was necessary to create their accounts. I doubt there was much affirmative agreement going on there.