Because most ads are done poorly, are manipulative, and hide the "real" cost of a service. It's also based on an increasingly outdated economic system that needs to change.
Really? That's still how most people consume content (news, social media etc) on the internet. You'd be shocked to learn that most people in Latin America for example use the ad supported version of Spotify and those with no Spotify in their country use ad supported pirate sites.
We still can have those or equivalent services without advertisements. We only use them because it's the model we know, not because it's the most appropriate model.
How do you know it's not the most appropriate model? Do you think Facebook and Google wouldn't switch to another more appropriate model? Whatever that means.