A fully-interoperable Java on smartphones IMHO would be a market failure out of the gate. The OpenJDK/JDK was designed for desktop environments, most of the API

A fully-interoperable Java on smartphones IMHO would be a market failure out of the gate. The OpenJDK/JDK was designed for desktop environments, most of the APIs left how have no applicability to mobile. To include them would needlessly bloat an already slow Java platform on mobile. These devices are extremely constrained by memory and battery. So, you can either have Java on 800 million devices where the APIs are subsetted and retargeted towards modern smartphones, or you can have a hopelessly bloated, too-many-cooks-in-the-kitchen JDK on devices no one wants to use, but they, they'd be capable of running Java apps from the 90s. This is like saying, I won't let you subset the Win32 APIs unless you guarantee that DOS 3.0 apps will still run.