Stating the obvious - because keeping them separate means Apple gets to double-dip on people buying more or less the same hardware twice.

I thought I wanted this. And in fact, I turned on the 'window' option for my iPad Pro when it came out. I did not, in fact, want this. The iPad just has totally different ergonomics, even with keyboard / trackpad / etc. Anyway, for years I've been convinced that would be the perfect combo - but in my own tests, - meh - At the very least, new hardware needs to be built that gives laptop-grade typing and trackpad. With that, then it would be upside - but I'm not sure that it would be that much cheaper than just having two devices.