I think insecurity, over-estimating difficulty / effort, and risk aversion are all to blame. I think these things would improve a lot if people have DIY tasks as part of their upbringing or education, if only to get experience with it.

But the education system - at least for me, 20ish years ago - was very much tiered or broken up into classism: if you were highly intelligent or a good learner you'd go to advanced schools where you'd get higher level math, latin, etc. If you were "dumb" you'd get taught how to do woodworking and masonry. At best I was taught how to use a figure saw, drill press safety measures, and how to patch an inner tube (welcome to the Netherlands, this is very important. Or, was, it's much simpler and cheaper to just buy a new inner tube nowadays).