Seems reasonable to me. Facebook is gathering what amounts to a static picture of each user then selling ads based on the pictures. There really isn't a time c

Seems reasonable to me. Facebook is gathering what amounts to a static picture of each user then selling ads based on the pictures. There really isn't a time component in the data (though perhaps they can add one now that the service has existed for many years). On the other hand, Google has more or less assembled a bunch of archetypes based on behavior (people who search for X later purchase Y, etc.). Then they match queries to these archetypes. The time component is front-and-center here because the archetype match was prompted by a user action. A purchase is really a time-related event that transforms the user in some sense. By purchasing something you're changing "who" you are from the perspective of an advertiser (e.g. a Chevy driver could become an Audi driver). So Facebook has a great picture of "who" each user is at a the moment, but no real way of knowing "who" each user would like to become or when. Hence, perhaps, some of their difficulty in selling ads. Or not.