As others have mentioned, lack of geotagging, wireless connectivity, and other convenience features made them poor competitors to smartphones. And it wasn't just wireless connectivity being behind the times, Canon's T7i (aka 800D) launched in 2017 still made you find a mini USB cable. They were good at optics, but dropped the ball on the rest of the product.
Even though the phone had worse quality pictures, it brought many other things to the table.
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 :(
"They sell tools not toys" - no offense, I hate deceptive UX engineering and e14n as the next guy - and vibration motors in Dyson vacuums - but that kinds of denials existed, and IMO had hamstrung Japanese tech products for too long.
"Piddly old wifi" is part of the problem, it's certainly what I'd expect camera vendors to support. You can push multiple gigabits over a good wifi connection these days.
If any camera companies are reading this, you probably read "I wish my camera came with a purpose-built app specific to your brand of cameras manufactured in 2024 (to be EOLed and replaced by a different app next year) and reimplementing an entire photo library with sync to your own subscription services because your manager says you need subscription revenue," but no I'd just like it to join my house's wifi network and give me a button on the computer to copy the files to a folder or add them to my Photos library.
