Java-gradle-plugin gradleApi() api dependency problem

By the document:
https://docs.gradle.org/current/userguide/java_gradle_plugin.html
the plugin java-gradle-plugin adds the gradleApi() dependency to the api configuration.

I developed a Gradle plugin by java-gradle-plugin:

However, I find if I remove the line implementation gradleApi() from example/build.gradle, the example will run (./gradlew :example:run) to fail with the errors

Exception in thread "main" java.lang.NoClassDefFoundError: org/gradle/tooling/GradleConnector
        at com.github.MrRogerHuang.GradleProjectRunner.run(GradleProjectRunner.kt:33)
        at com.github.MrRogerHuang.GradleProjectRunner.run$default(GradleProjectRunner.kt:32)
        at com.github.MrRogerHuang.ExampleKt.main(Example.kt:6)
        at com.github.MrRogerHuang.ExampleKt.main(Example.kt)
Caused by: java.lang.ClassNotFoundException: org.gradle.tooling.GradleConnector
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
        ... 4 more

I check build/publish-generated-resources/pom.xml generated by ./gradlew publishPlugins and find there is no dependencies tag related to any Gradle API. Why does java-gradle-plugin add gradleApi() api dependency, but not generate any dependencies tag to pom.xml?