I can imagine say, readers of Golf Digest are probably interested in golf. That's about the extent of the research that can be done by a traditional magazine. But there's an entire ad industry (for better or worse) to minimize 'wasted' impressions, and there's a large chasm between "male 25-35" and "specifically John Doe who looked at #9 clubs yesterday but hesitated to buy them, maybe we can win him over". Clearly the later example is prohibited in the spirit of the GDPR, but it's broad enough that it kills the former as well (and puts the extent of information available to the industry back to "golf digest readers play golf").
Not that I am particularly sympathetic to advertising agencies and the machinations of what online ad-tech has become, but I am sensitive to legislation that puts entire industries (I.e. real people's jobs) under a coal fire of "maybe we as a company literally have no viable path forward".