The Gradle plugin is currently only published to the Gradle plugin portal.
Publishing it on MavenCentral is easy to setup.
Main reason to consume the plugin from MavenCentral is the JCenter shutdown and the redirection handling of the Gradle plugin portal regarding proxying MavenCentral, https://blog.gradle.org/portal-jcenter-impact.
That's why we do not depend on the Gradle plugin portal at all but only use MavenCentral.