Comment by asmor

They adopted declarativeWebRequest as the exclusive option for "content blocking" years ago, which requires an actual extension update to change blocked URLs. It allows for some optimizations that look nice on benchmarks, but in reality uBO makes the web faster by getting rid of a lot of tracking requests and javascript. Nobody in the ad industry cared, because Safari's share is so small and plastering Safari users that use this basic adblocking in ads probably would've made them move elsewhere.

Chrome doing this however changes the value of working around adblockers, because they now lack the ability to rapidly respond or match with code (that's not regex) or even reading a bit of the response.