I tried adjusting my own derailleur once.

Shop for me from then on.

The full quote is, "A lot of them now will come to cycle shops for pretty much 90% of bike repairs." So not necessarily that 90% of people are coming in for every issue, but that there are people who rely on the shop for almost every issue.

I've learned a lot about bike repairs this year, and I've been volunteering as a mechanic at free bike repair events. It's been interesting going from the clueless customer asking for a "tune-up" to being the one asked for a tune-up. If you ride but don't have maintenance background you know that it's possible there might be some problematic, or even dangerous issue; but you have no idea what that might be. And if you can identify a problem, as far as you know any work you do might brake something in a way you don't understand. So I can understand people going to the shop frequently.

I'm surprised when I talk to people and almost always hear that they bring their bike to a shop for maintenance and repair. I'm usually the strange one who do his own maintenance and repairs. So I can believe that most people bring their bike to a mechanic. The 90% figure still seems high though.

I think it is fairly common for the average rider in a bikeable area. Like a car sure a lot of drivers know how to change a tire, a lot fewer change the oil or brakes. Computers arent hard to build but 90% of people buy something premade.