Remember the adage “divide and conquer”? If you want to destroy something, consolidating its power base (like GDPR does to advertising in Europe) is a poor first move.
The GDPR doesn't only apply to advertising companies. When you're offering services in exchange for money you still have your customers' names, IP addresses etc. Even if you aren't using any of that information for advertising or data mining, you still have it, which means you still have the compliance cost. A lot of that cost is not proportional to how much data you have or what you do with it.
And that's the problem. The GDPR will never destroy Google or Facebook, but it can destroy a three person startup that has nothing to do with advertising and might have offered an ad-free alternative to some of their services.
If destroying the ad industry is the goal, why not just tax advertising at >90%?