The short hand answer I’d try to give people is ‘it’s statistics’. Based on training data, there’s a certain chance of certain words being in proximity of each other. There’s no reasoning behind placement, other than whatever pattern is discernible from known situation.
There’s nothing technically stopping you from building an android smartphone just the way you like. In fact, there’s extreme modding folks that do things like already. What we really lack is a future-proofed connector standard for component connectivity that just works.