Disclaimer: I work for Google but not on any of the ads teams. This is a personal post.
When Pete Snyder filed WICG/webpackage#551 that Web Bundles might break ad blockers, I had to figure out what makes those ad blockers work in the first place.
Now, obviously, if a page loads an ad from a URL, then blocking that URL will block the ad. But the web is an evolving system, and ad blockers are in an adversarial relationship with publishers, advertisers, and ad-tech companies who all want to make sure users see their ads. Those ad folks are smart and capable of finding ways around naïve attempts to block their ads. So what prevents them from avoiding that list of URLs? Why do URL-based ad blockers keep working?