Honestly if every brand would stop making their own shitty launchers and filling their phones with bloatware this would mostly not happen anymore I think. Pure Android on Google Pixel phones is hands down better than every other version.
The Samsung's OneUI is imho much better than pure android in terms of features and UX. It's sad, because it shouldn't be like that and it makes it hard for me to leave samsung for something else (I wanna pixel with GrapheneOS)
Because of privacy (not only Samsung's, but Android itself sends massive amount of data to Google)
GrapheneOS removes all the tracking and hardens the android to be more secure.