Do you mean dual-booting macOS and iOS? If so, they probably don't because it would work like crap. The tablet is a touch based device and macOS isn't optimised for touch. Unless they want to release something very janky they'd need to invest a lot of time making macOS more touch-optimised and I think the number of people that would care about that or use it is miniscule. The tablet and laptop are completely different form factors and have completely different use cases. Making both devices capable of doing the same things would just unnecessarily compromise the design of both.