I am a Computer Hardware professional. I started working with computer technology in the early eighties. I have seen the evolution of technology starting with closed platforms like the game console era and then the move toward open platforms like the Home Computer Golden Age. In the last 5 or 10 years, I have witnessed technology changes that are slowly moving away from open hardware designs towards hardware that is locked down and can’t be modified by the user.
Dell blocking the BIOS is a bit slim to claim “PC hardware companies”, but they definitely are. HP’s crap too in this regard.
Cramming more and more stuff into a SOC leads to this for sure but it’s hardly the only factor. Built-in obsolescence also plays a heavy role.