Because server side tracking isn't sufficient? I've heard from numerous people that it definitely is. Tracking cookies are a massive privacy invasion for what is minimal, if any, benefit
Even if your site is set up well to support it there is objectively less data you get back. Like it's hard to figure out where are the trigger points that increase or decrease conversion all that stuff. Or if people leave and come back. And it's a lot harder to run your own analytics (coming from somebody who does) even if you are just hosting somebody else's solution.
Setting up all the random shit gdpr requires (downloading and deleting data, protection officer blah blah blah) takes a lot more than a cookie bar. It's expensive and if the site doesn't make much money from europe, why the hell would it waste money on doing that?
Edit: I used archive.org to read the article and copy-pasted it here: https://gist.github.com/SkyfallWasTaken/55b9787a7bda35f839a0...