It might be that personalised ads are only marginally better (if at all), but the perception of the advertisers and publishers is that it’s very important, thus

It might be that personalised ads are only marginally better (if at all), but the perception of the advertisers and publishers is that it’s very important, thus creating a (fakeish) moat for Google, as it’s more difficult to execute. Or maybe that’s really not that important, as the biggest moat remains Google being number one web destination.