Because of the depreciation curve, a $500 computer is almost worthless after several years while a $1000 computer might be worth a hundred or two hundred dollars. Do you spend $200-300 on your $500 computer for say memory + SSD or put that $200-300 towards a new $1000 computer?
As far as time is considered, engineered solutions are generally read-to-go, Apple or Windows, but the Windows world still seems to be rife with bloat. Navigating the hundreds of models & manufacturers is overwhelming for the non-technical user. For many technical folks, it's much simpler to just say, 'Get a mac' or 'Get a Dell', nut the Dell option will be a small pain with navigating the choices.
Non-engineered solutions (building your own) do cost a little bit of a time investment in research, assembly and tweaking. For the technical folk here, it's merely a couple of extra hours. For the uninitiated, it's a lot of hours for knowledge that may not be readily applicable to them on a day-to-day basis.
I absolutely guarantee you that there simply are not enough of you to make hardware manufacturers cater to the upgradable/repairable market.
The only way upgradability/reparability will continue is if people like yourself form a non-profit or B Corp that makes open hardware that allows for it. The vast majority of people don't care.
This saves me time for my wife, my children and my hobbies. It also saves me money. Time, and money, to spend on what's important to me. It also sends a signal to companies: there is a market for upgradable, repairable hardware.