Never had an issue setting mine up when I had one. Watched a couple youtube vids, and it was like a 15-20 minute setup with string change from then on.
The answer is, they never learned how. Which isn't an excuse now with the whole interwebs and 18 million videos on the subject.
I would also acknowledge that some people just are not handy or mechanically inclined .The simple act of a screw driver adjust is like watching a monkey fuck a football.
When I was 15 I lived and learned how. Biggest mistake I made was taking off all strings not blocking. Now days. One sting at a time. Very minimal adjusting
Same with pickups. I swapped out my first at 15. No idea what I was doing. Haha
Just had the guitar plugged into the amp. Kept moving the wires until it was clear and loud no buzz. That. Took me a while ?
I learned to do this stuff as a teenager growing up in the 80s and have been thankful with that I have learned over many years with regards to guitar setup and repairs. It's been a great side job to make some extra $$$. I have quite a few friends with very large collections and they are always calling or dropping off guitars for things to get done or changed.