I think there's an unspoken rule on the internet: any piece of personal data will eventually be used for ad targeting.

The response rates for display ads are so abysmal that any edge can make a difference. CTRs (click-through rates) hover around 0.1%, so if you increased CTR by a slim 0.1%, you'd double the revenue!

The corollary (?) is that the most unexpected use will likely be the most lucrative.

I literally LOL'd at this :) .