Because the easiest argument against tech giants is “they hurt children”. If the tech giants can ‘prove’ they don’t serve children the argument is gone. So the techs are lobbying for age verification. They don’t even care if it works, when it is not their responsibility. Of course the problem is not about the kids only, but the whole business model based on advertising, data collection and manipulative algorithms. But it is easier and better for business to age verify and ‘ban social media for kids’ than to fix actual problems.