Yeah, your browser fingerprint might be a needle in a needlestack. You might not be able to distinguish one needle from another needle easily, but if you have enough needle samples you can start to identify what the needles are pointing at. Data aggregators collect enough pseudo-indistinguishable needles to be able to disambiguate and associate them with a known identity or cohort. For example, your mobile browser might be indistinguishable from most other Mac users in Brooklyn, but your mobile browser might be the only one running on a device from an IP address that regularly logs a meal in MyFitnessPal at that Starbucks wi-fi before making Apple Pay/Google Wallet purchase, hits the next 8 stops on the train before connecting to the same cell tower at the narrow window as you enter your office (telling on myself a bit, tho I am in Vancouver, not Brooklyn).

Span this across all of your movements and activities across multiple aggregators and it's a trail of movement through a fog of data that is fuzzy, but enough to identify you, or a small cohort of similar users.