Why? Economics: removable CPU card makes sure that you can keep using the same big plastic case for a longer time, which makes it cheaper on the long run. You can also easily have a different OS on different cards and swap between a work and a private laptop, or a separate CPU card for each of your children. Or vice versa, use the same CPU card for different size tablets.
Why does Luke do it? Because nobody else does. Big companies are saying that it’s not economically viable for them. However, Luke predicts that very soon there will be another crash like in 2008 and this time the prices of products coming from China will increase dynamically. In such a context, the replaceable CPU card concept becomes extremely viable.
The idea is to mass produce the CPU cards in China cheaply, but manufacture the tablets/laptops around it locally to avoid shipping costs.