There's lots of reasons. 1 - google is the only company (bing to a much much lesser extent) with access to primary search data. If you believe that the origin

There's lots of reasons. 1 - google is the only company (bing to a much much lesser extent) with access to primary search data. If you believe that the original pagerank algorithm is too easy to fool and that it has been massively deprioritized in favor of gathering intent data created by user actions on google, this makes them a natural monopoly. Any other attempt to gather the data to make intent targeting work will be hindered by the lack of consumer touch points. 2 - see consumer touch points above -- very few companies have them. Eg the new eprivacy law (depending on which draft -- there are conflicts between Council / Commission / Parliament), will be a virtual monopoly guarantee for FB / Google / yahoo. One of the features is that company 1 can't ask for consent on behalf of company 2, so, again, only companies with an end-user touch point can get legitimate consent. Thus all 3rd party adtech dies. This seems in direct conflict with pro-competition rules in the EU. 3 - Adsense also becomes much harder to compete against. Google does intent extraction -- buttressed by the data from search -- better than anyone else. You can, of course, attempt to compete algorithmically, but you lack the data. 4 - GA allows to extract behavior post click from within the site. No one else has this. You don't even really need personal data for this to be amazingly useful; merely aggregate is very powerful.