@joeo10 you're pointing out an issue that almost no one cares about or at least they rarely think about upfront. Whether they should is a different question.
This is also not a phenomenon unique to personal computers. Practically all consumer electronics are not easily repairable or upgradable. If they are, it is generally cost prohibitive to do so. As my step father was an electrical engineer who made a living repairing computers and other things, I watched this change happen up-close in the 80s and 90s.
As a personal project, sure, give me your old computer. Most people won't bother, though. Not everyone grew up building and fixing computers, making me totally comfortable opening the case, swapping components if needed, and reinstalling an OS. This is how I get new hardware in general: as hand-me downs.