Well they based most of their original implementation on Apache Harmony. Just speculating here but it may have been due to dates. OpenJDK's first release was ~2

Well they based most of their original implementation on Apache Harmony. Just speculating here but it may have been due to dates. OpenJDK's first release was ~2007 but IIRC the original pre-Google Android team started work in 2003 or 2004.