Agree with vbezhenar that Apple doesn't really budge the needle to make this happen. And then you have vendors like Dell that are specifically catering to the Linux market.
Yes, but what prevents Dell from becoming more like Apple, e.g. by installing vendor lock-in features at the BIOS level, or work with Intel to install such features at the CPU level.
Also, you can buy a GPU but in some ways it is locked down (by NVidia), so as technology progresses we might be moving away from the "generically useful computer" model.
Because competition. It would only limit their market, not increase it. Dell competes with other laptop vendors in this "generic" market vs. the lock Apple has on their OS. And do you really think Intel would work with one specific vendor in this space to given them exclusive CPU features that nobody else would get?
NVidia has always been locked down so that is not news. If you are concerned about the GPU, buy AMD and enjoy their open drivers. Intel is entering this space too with open drivers as well. And who knows, perhaps NVidia might be opening up a bit after all vs. going the other way?
Also, you can buy a GPU but in some ways it is locked down (by NVidia), so as technology progresses we might be moving away from the "generically useful computer" model.