WatchOS is hardly embedded though. An Apple Watch is basically a small iPhone tied to your wrist in terms of architecture. That’s got a whole lot more in common with a full desktop computer than it does with a microcontrollers, where they often have rather weird architectures by desktop standards, and it’s quite rare to have MMUs and things like that. Also, there is no underlying OS, and no heap allocator (unless you provide one). That’s the kind of challenge that an embedded language runtime has to provide.