Of course they do, but people pay crazy money for this and it plays the important role in Google's market valuation, so it's in Google's best interests to continue chanting the Big Data Big Money mantra. It doesn't help that the myth/meme is strongly backed by the whole cyberpunk genre, as people love the dystopian themes of "big corporations know everything about you, down to your most secret desires you don't even realize yourself".
And it probably even work by some small but statistically significant margin, compared to some arbitrarily picked baseline, so they can even back this up if necessary.
The king is naked, though.