This is exactly right, but I fear the incentives have changed and we'll never again see something like the x86/IBM-compatible/Wintel world of "standard" inter-compatible systems.
As you say, it's a "why bother?" problem, and no manufacturer will want to bother: Apple has no interest in making it easy to run other OSes, Microsoft wants to sell you "Windows Surface" devices, not general-purpose computers, corporate buyers want a "secure" locked-down environment with a signed bootloader...
Are there any powerful stakeholders who benefit from interoperability?