Even when discussing just the on-camera UI, there's nothing about "tools for professionals" that says they must never change the UI, or that every setting must be immediately accessible in a flat hierarchy, or that you must use a one-axis scroll wheel to change a 2D focus point, etc.
Yes, it's a great thing that there are features of a standalone camera (like instant on, or physical buttons) that smartphones don't have. However, that doesn't mean the cameras have to disregard all the UX and UI changes other electronics have gone through over the last 10-20 years (some good, some bad, but over the long term they've become more approachable to more people). Meanwhile cameras remained largely unchanged and as a result DSLRs are pretty much a dead segment now. (I too loved the viewfinder and ability to use them without an screen, especially when optical... but not the rest of the experience).
As a former amateur photographer, I eventually sold all my bodies and lenses because it was just such a pain to use them compared to the smartphones and prosumer prime compacts of the day, which were all iterating much faster than the "proper" DSLRs. Back in those days, even just getting the photos off the camera wirelessly was a pain, requiring the use of 3rd-party WiFi SD cards or really old USB cables. I think these days mirrorless is once again trying new things, but I'm out of the hobby now and can't afford to reinvest into it :(
