As someone who fixes basically everything until you can no longer tell it is a ship of thesis, I don't think complexity or safety features are the problem so much as not designing for or expecting someone to fix something in combination with extreme penny pinching in manufacture, so that there isn't enough material to anything for repairs to be done reasonably. If something breaks, the original material was at such a bare-minimum thickness and/or low quality alloy or plastic to start with that even the smallest defect in repair is a problem.
Its like trying to fix a single broken strand in a spider web, even with the tiniest thread you can find and the most delicate hands and tools, any manipulation of the web at all is likely to cause even more defects and any successful patch job will need to be way over-kill compared to what was originally broken. You can't just fix that one thread that broke, you gotta throw a large patch over the entire area and hope that the original spider thread designs that were undamaged will be able to hold up against your much stronger patch job.