It’s not just skills not being passed down, but also that as technology has moved on, things have got more complicated, and then the skills needed to figure out why something isn’t working, and what needs doing to fix it plus actually carry out the fix, have got more and more technical, to the point that anyone who could do a repair could also probably get a much better-paying career than repairing things.

That’s not an inherent problem, as a good service manual from the manufacturer could bypass the need to understand all the details of how a device works to identify a root cause, but it’s not in most companies’ interests to provide one that good when regulation doesn’t force them to, so for the most part, things need repairing without help from the manufacturer.