I think its because Google isn't afraid of them in the least.
It also is probably a decision made to prevent monopoly complaints. If they were to stop ads for Brave or other browsers showing, using their advertising arm either on Youtube, or the web in general, it would bring attention to and provide an impetuous to break up Alphabeta (Google's parent company) for being too broad.
Its not good and one imagines the test with restricted data is something only until they unlock it all. And these restrictions are still very broad -things like Eye tracking still seem likely to be tracked, and in my opinion that might be the most dystopian option of the bunch. Using eye tracking to serve product placement and ads in perfect spots...
Facebook is about the worst company to have a leadership position in VR.
It also is probably a decision made to prevent monopoly complaints. If they were to stop ads for Brave or other browsers showing, using their advertising arm either on Youtube, or the web in general, it would bring attention to and provide an impetuous to break up Alphabeta (Google's parent company) for being too broad.