Because they could improve your life. To come up with good examples, one would have to know more about your preferences.
But imagine there's an event (party, fair, game jam) and the only way to know it's happening is to specifically search for it, there are no posters or advertisements online. Don't you think that some people that would have wanted to go would miss it because they never even noticed that there was an event?
> one would have to know more about your preferences
And creepy/stalking advertisers grab all they can learn about my preferences. That's the state of ads on the internet for the past 20 years and I have never seen it "advertised" (haha) as a good thing.
But imagine there's an event (party, fair, game jam) and the only way to know it's happening is to specifically search for it, there are no posters or advertisements online. Don't you think that some people that would have wanted to go would miss it because they never even noticed that there was an event?