It is a marketing strategy that in starting companies give access to their platforms free of cost and after sometime when they get users they start charging them as we see Facebook charges amount when users verified their profiles same goes with snapchat. And yes Facebook sell advertisements space to advertisers and in return Facebook generate revenue.
That is right, it is a marketing strategy and I think everyone is shown to the terms and conditions before they sign up. The revenue that they generate is because of the users but they have infrastructures that are open to everyone and I think that's the best product that they can offer for free in return of their revenue. Whilst for the verification, it's not that much at all because they have copied the idea to Twitter now X to have those verified badges but it's another source of revenue for them.
Most of the time, users don't read the terms before signing up. Usually, they will only check it once they got into trouble. And of course, it is already too late when that happens, because either your accout is frozen or suspended and your funds are being "hostaged" for you to comply with their requirements.
I am guilty of that but at least I get to check some clause of it but they're all the same that they have the means to do whatever they can with the data they've collected from us. They could send it to the advertisers but at most times, they'd only say that they are going to protect it and they'll keep it safe. There is no transparency in there but as a regular user, who cares right? as long as I get to use the platform and registered on it and can contact all of my highschool and college friends through it. Just be a responsible and disciplined user, overall in the internet and not just with these social media platforms.