Because the direction Chromium is heading is in large part controlled by Google, more than Firefox. Also Chromium still has Google bits, otherwise ungoogled-chromium won't exist right?
I see. I generally agree with that, which is one reason why I'm a Firefox user, but I'm not totally sure I buy it as a reason not to use Brave. It's a fair viewpoint, though. I could see it being a reason for being against Brave if the Google-ness of Chromium is able to make Brave less private.
I think Google recently took out the syncing capability from Chromium. Things like that.
Edit: Also the manifest v3 thingy which made Ublock Origin operation restricted, also I think it prevented CNAME uncloaking. Idk whether Google went ahead with manifest v3 though.