Sometimes the obvious answer that the ad company wants to limit its browser's ability to block their revenue stream really is the correct one. The technical reasons they've given have all been clearly working backwards to find justifications.
https://github.com/w3c/webextensions/issues/302
(By the way, the meeting minutes are all published so you can read exactly how they're conspiring to kill your privacy and security. Take note of how many times they decide not to implement something citing that they don't want to engage in a cat-mouse game. How benevolent of them, to make the hard decisions on our behalf.)
Googles brand is becoming more and more toxic, from my perspective.
Thankfully you can turn it off.