why there is no support of external jars in intellij based plugin jars?

We are having an issue where our plugin uses an exernal jar. Its a gradle plugin. We have externally added the depenncies too in build.gradle file and created a plugin jar out of it. But when we place this plugin jar in the installation folder/plugins/abcpluginJar/lib/abcplugins.jar our features where the external jar is used doesnt get picked up and no class def found error is thrown. but if we place the external jar along with abcplugins.jar then our features work perfect. Why are we not able to package the external jar and not use it externally for making our plugin run.