Even after they dumped Apache Harmony for OpenJDK, they only cherry pick what they feel like from OpenJDK, relatively easy to check, comparing the AOSP source code with OpenJDK.

Then there is the whole history of what ART can do, versus the native JVM bytecodes, where some features are lost in translation, e.g. lambdas aren't nested classes, they make use of invokedynamic.

Additionally they are in no hurries to update Java baseline version, other than when Kotlin starts losing access to more recent Java libraries at Maven Central.