Because usually reimplementations are done in a way that would allow programs&#x2F;libraries written for the original platform run on your platform, i.e. reimplementations are usually done in a way that makes them drop-in replacements to the original as much as possible. That is not the case with Android. Running existing Java programs is a non-goal, and reusing libraries is only a goal as long as it helps Android&#x27;s separate ecosystem (Java libraries -- for any Java standard -- work on Android only if they happen to use the subset of APIs implemented by Android; this is not due to any real limitations or lack of developer resources, but simply because being a drop-in or near-drop-in replacement for Java is not a goal for Android).<p>I will note again that Google is free to use OpenJDK <i>however they like</i> -- they don&#x27;t need to be compatible or anything -- as long as they comply with the GPL license.