user20583982 That's what big tech is trying to accomplish. They're trying hard to keep us excited about bells and whistles rather than come up with something which genuinely improves our lives. Most of the ground braking tech is 10+ years old so nowadays it's more or less just eye candies.
I have to actually heavily disagree. UI creates more accessibility and integration, nor should we associate the actual work put in by UI devs to 'big tech', these are normal every day people who drive home to their house like any other person.
We have also had enormous amounts of technical advancements from mathematics (Machine Learning, post-quantum encryption which works on a much more head-wall banging method than ECDSA/RSA. Genuinely look up some of these RFCs they are painful), computer engineering, software engineering, and internet service maintenance that has become wildly more accessible and useful.
GrapheneOS doesn't really 'polish core functions', I am not sure what you mean by that. Android does a lot of different things. GOS just hardened the already existing code of Android and patched certain oversights and concessions that were made.
Yes not every UI change is important, but its not some conspiracy, UI is a function of usability and adoption. Design is an important aspect of software engineering and its usually its own department with its own funding in large projects like AOSP