But they feel the need to spend money on 3rd party AVs, money that could be spent on something actually useful. The AV companies heavily advertise that "you're not safe unless you install this AV".
By installing 3rd party AV they increase their attack surface too. New program, lots of files, all of them can introduce more vulnerabilities, bugs etc.
I was in the same boat actually, but then decided to put a stop on that and made the repo. I didn't know Windows had all those features and thought I really needed to install an AV to keep me safe. That's why I want to help others not to fall for the fake advertisements.