The advertising infrastructure is largely funded by the big advertisers, and legal issues certainly matter to them.

When (for example) Toyota is paying a bunch of money to target customers in France, they're playing with the same rules as Ford is when targeting the same customers. They don't have to do things against the law to compete in advertising, and they'll even be eager to identify competitors breaking advertising law to screw them over; there has been lots of legal action taken as a result of such industry self-policing to ensure that competitors aren't able to benefit from misleading advertising.

Sure, there are lots of businesses who would by "under the table" data and apply it illegally, and it is a huge advertising market - but it's absolutely dwarfed by the much, much, much larger advertising market funded by the major international public companies. The advertising money flowing from a single company such as Procter&Gamble or Nestle is larger than all the total advertising turnover from whole smallish industries. If you cut off the tracking-adtech companies from the legal market, it's like restricting oxygen for them - they'll still have some customers, but they'll get an order of magnitude less money to do their things.

Actually, in that case the centrality or Monopoly of the Apple store and the Google play store makes regulation easier. Censure Apple or Google for the apps sold in their marketplaces that violate the law and they will be taken down.