I'm mostly speculating but, they wouldn't be selling the data, they would be selling access to their ad network that has models built off that data used to match ads to people. If they have a high(er) conversion rate, they can charge quite the premium for this information. Similarly, if they could merely keep people in their platform (WhatsApp), nobody else has that information -- same effect.
(Also speculating) if that's more or less how it works, and an ads conglomerate like Google or Facebook is worth hundreds of billions, then even a fine of a billion dollars wouldn't be enough to deter them from this activity.
None of this is meant to stir up controversy or be negative or anything, I just think its an interesting mental exercise to consider this scenario and these motivations.
(Also speculating) if that's more or less how it works, and an ads conglomerate like Google or Facebook is worth hundreds of billions, then even a fine of a billion dollars wouldn't be enough to deter them from this activity.
None of this is meant to stir up controversy or be negative or anything, I just think its an interesting mental exercise to consider this scenario and these motivations.