Enforcing the use of JDK 11 on release guarantees that the published Multi-Release JAR contains ALL code versions: JDK 8 (default fallback), JDK 9 (enhanced NIO) and JDK 10 (even further enhanced NIO). Without this enforcement, there would be a risk of not having some of these versions packed into the MRJAR due to the way the POM checks for the existence of supported JDK levels using JDK-enabled profiles.