it's important to remember that google's goal isn't to track you, it's to make money. So finding something that works better isn't necessarily a better way to track you, just a better way to make money.
tracking, including the costs of collecting and storing all that data as well as the PR cost of people being creeped out by all that data you store, is expensive. Given how accurately i'm targeted by most advertising (not very) it seems perfectly reasonable to assume that ads will be just as effective and just as revenue-generating if their tracking becomes a bit less granular.
it's the same end result though - whether they don't have the ad inventory to make use of hyper-detailed tracking, or they're just not very good at turning the tracking into targeting, then either way performing the hyper-detailed tracking is a waste of money and they can make more money by spending less on tracking me.
tracking, including the costs of collecting and storing all that data as well as the PR cost of people being creeped out by all that data you store, is expensive. Given how accurately i'm targeted by most advertising (not very) it seems perfectly reasonable to assume that ads will be just as effective and just as revenue-generating if their tracking becomes a bit less granular.