I'd say nothing, Wayland is used on mobile and embedded, the reason Canonical made Mir was so that the had full control/ownership of the display solution and thus could charge a license fee to proprietary vendors who wanted to use it.

Nothing inherently wrong with that, but for someone outside of Canonical it's hard to be interested in a competing solution which only exist in order to pad Canonical's bottom line.

Which was also the reaction from the rest of the Linux ecosystem.