There are technical reasons, but as ever the real underlying causes are incentives. Companies realized that the OS is a profit center, something they can use to influence user behavior to their benefit. Before the goal was to be a hardware company and offer the best hardware possible for cost. Now the goal is to own as large a slice of your life as possible. It's more of a social shift than a technological one. So why would a company, in this new environment, invest resources in making their hardware compatible with competing software environments? They'd be undercutting themselves.
That's not to say that attempts to build interoperability don't exist, just that they happen due to what are essentially activist efforts, the human factor, acting in spite of and against market forces. That doesn't tend to win out, except (rarely) in the political realm.
i.e. if you want interoperable mobile hardware you need a law, the market's not going to save you one this one.
My guess is that modern hardware is too complicated for one hacker to write reliable drivers. That wasn't the case back in the 90-s, when Linux matured. So we are at mercy of hardware manufacturers and they happened to not be interested in open upstreamed drivers.
On any PC, you can still use BIOS/UEFI services to get a basic framebuffer and keyboard input. You cannot do that on embedded ARM devices - you need to get several layers into the graphics stack to have a framebuffer. I tried it on the PinePhone, using existing source code as a reference, and the furthest I got was sending commands from the video port to the LCD controller and then not having an oscilloscope to see if the LCD controller replied back.
Having basic framebuffer in BIOS/UEFI is neat for toy OSes, but not very relevant for something practical. You gotta need proper driver for GPU. And if you're just starting, UART console is actually more preferable way to interact with board, IMO.