Because money, and because we've let advertisers get away with it since at least as far back as colonial times. People still accept it; they complain, but their dislike and discomfort aren't strong enough to motivate them to look for alternatives. People still use Windows - even those people whose needs would be fully served by a Linux box. They still use stock browsers without ad-blockers and other readily-available extensions that would give them some degree of privacy. They still flock to Facebook.

For the greatest part, humans lack either analytical capabilities or the urge / curiosity to apply them to their own lives and their own culture. They see ads as mostly annoying, sometimes entertaining, but ultimately harmless. Most don't understand that the primary accomplishment of advertising isn't simply that it convinces some people to buy a product they see in an ad. Advertising targets people's insecurity and inadequacy, and then dupes them into believing that purchasing something will make those bad feelings go away. And buying in does make them feel better, for a short while. Then the bad feelings return... Advertising has shaped our daily experience, our view of our own world and ourselves, in ways that few people even notice, much less comprehend.

As far as I'm concerned advertisers are exactly analogous to pushers. They get people hooked on things and behaviours that are ultimately destructive and life-denying, both to themselves, their fellow humans, and the planet - and they do it out of pure greed. But then, corporations are psychopathic - how did we ever expect any other kind of behaviour from them?

Germany promised to stop annexing territories after the Munich agreement.

A promise is no more trustworthy than whoever makes the promise.