It isn't so much a technical issue as it is one of trust and efficiency. GA is familiar, and easy to compare across different sites without worrying about how e

It isn't so much a technical issue as it is one of trust and efficiency. GA is familiar, and easy to compare across different sites without worrying about how exactly they're mining their logs. At best, they have to figure out how to make efficient comparisons. At worst, they have to worry about sites inflating their numbers--either through fabrication or just optimistic tweaking of how data is presented. With GA, they don't really have to worry about outright fabrication or reliability. And while there's a ton of data to be teased out of server logs--especially if someone tries to correlate it with other user data they already have--for most advertisers, that doesn't really matter. They don't want to invest the time it'd take to make use of it with all potential properties they want to advertise on. Say what you will about GA and privacy issues, there's a reason why it's become so common place. Not just for site owners, but advertisers as well.