Earlier quoted context omitted.
The same way it used to work: you show the same ads to almost everyone based on the content, not the people. Not that I think advertisers will go for it.
That's considered "spray and pray" today. Today advertisers want data, data, data, and micro-targeting is everything. The entire advertising industry has become something akin to a private signals intelligence agency.
And even with all that, the most of the targeted ads aren't any more compelling than content-based "spray and pay."
IMHO, targeted ads are pointless unless they're a targeted to a search query.