You make several good points about knowledge coming from older generations and from tinkering. It’s worth expanding a little because I think cost is not the reason. Like another user said, computers and cars were always expensive. TBH today it’s cheaper than ever to learn how computers work with the existence of micro PCs like Raspberry Pi. Furthermore kids today have a massive advantage in how easily they can access information. You can learn how to do almost anything by searching a tutorial on YouTube, and then any questions you can ask in some oddly specific reddit page. All that used to be go to the library and maybe, just maybe there will be a current book on it, and the librarian won’t know specifically how to help you.

I think it is a combination of a few factors:

• Less drive to innovate. Most common problems are solved, you can just buy an app for like $1 if it’s not free. People fucked with their computers in the past because a solution wasn’t available.
• Intentional proprietary lock-in / black boxing. As mentioned by others, software vendors have gone out of their way to force interaction through custom APIs, or no API at all, instead of conforming to standards
• General capitalist specialization of labor. The skills needed to do meaningful development in the current world of tech requires highly specialized therefore siloed knowledge.