Gradle dependencies does not show all dependencies

A specific jar dependency makes trouble in my Gradle project and I want to figure out the reason. My Gradle project is based on https://github.com/ghillairet/xcore-gradle-example and I use Gradle 4.8. I remove my ~/.gradle directory and run ./gradle assemble. In the output I can see that e.g. the following jars gets downloaded.

Configure project :

Download https://jcenter.bintray.com/org/eclipse/platform/org.eclipse.equinox.common/3.8.0/org.eclipse.equinox.common-3.8.0.jar
Download https://jcenter.bintray.com/org/eclipse/platform/org.eclipse.core.runtime/3.14.0/org.eclipse.core.runtime-3.14.0.jar

Task :generateXtext

How can I figure out the reason why these jars are used? I run gradle dependencies but there is no dependency to the files above.