I don't think it's much of a deterrent, because there's no clawback of the ill gotten gains from the use of that data. That's something done routinely in, say, fraud cases.
In effect this just encourages them to keep this practise going. This has to be treated like fraud.
Why isn’t anyone going to prison for this? Happens regularly with fraud.
This ruling should make it a lot harder for advertisers to hide behind the IAB though. One would hope that opens members up to more substantial fines in the future.