looks like rendering adblockers extensions obsolete with manifest-v3 was not enough so now they try to implement DRM into the browser giving the ability to any website to refuse traffic to you if you don't run a complaint browser ( cough...firefox )
here is an article in hacker news since i'm sure they can explain this to you better than i.
and also some github docs
I mean, there's the FAQ for this question among others, and it's like asking why Linux and not some Windows 1337 Pr0 B00tl3g Edition.
That "whole new piece of software" takes many times less than loading a webpage FFS, how often do you visit new webpages? And some people also play games, is installing a game a non-starter?