They just can't convert any BAT rewarded for ad participation into fiat right now.
It's on the roadmap though, but even then you'll have to go through KYC AML providers so there'll be no option of anonymous earnings.
When BAT is paid out to people surfing the web, does someone knows what ads they saw, maybe what webpages they visited to see those ads?
A user model is built on-device to allow for opt-in targeted ads, but that model does not leak across the wire.
Because the user model is not bound by a security sandbox, it can build a much richer model of user behaviour than even the most invasive ad-tech solutions that exist right now.
So Brave claims end-users get more relevant, targeted ads and more privacy, because this model can't be accessed off-device.
It sounds good in theory, and now ads are live we'll get to see how true it is in practice.
Would seem a really stupid move...