Tablets need to be very small, lightweight and thin. Making them modular and configurable would go against that. Look at some ipad teardown for instance and wa

Tablets need to be very small, lightweight and thin. Making them modular and configurable would go against that. Look at some ipad teardown for instance and watch how everything is packed together. Not to mention that these days everything is in SoCs: you can't upgrade the GPU and CPU separately. Even the RAM can be stacked on the SoC package and if it's not it's soldered right next to it. Contrast that with the innards of a desktop PC which is mostly empty space.