This is obviously about profits. You can make a macbook pro that has a touch screen....when you detach the display, it goes into iOS mode. There's your hybrid with no loss to anyone except apple profits.
Except you now have a detachable display that must have a:
1) large enough battery to last as long as it does docked or people will whine about battery life...
2) large SSD in it so people don't whine about not having enough room for all their data and programs and having to decide what to load onto the display before detaching it...
3)powerful enough processor to run programs as fast as when docked or people will whine it is to slow...
4)fan to cool the thing and give people fan noise to whine about...
5)way to convince developers to rewrite programs to work with a touch screen or else people will whine "Why can't I play X when I detach the display..."
6) set of port s that replicate the base unit's or else people will whine how that can connect a USB device or external monitor...
The list goes on, but my point is to make something that meets people expectations would require so many tradeoff start the result would be a great big metal and glass chunk of hurt. People would expect the display to function like a laptop when detached, not to magically become an iPad with fewer capabilities and different programs.