The current default /home/jenkins causes some issues in some scenarios:

When building a docker image with kaniko that is actually a jnlp agent image, since the specified workingDir is mounted as a volume in all containers in the pod, and it is also the home directory for the jenkins user, it prevents adding any file to /home/jenkins in the docker image.

Changing the default working directory to /home/jenkins/agent should not have any downside except for users hardcoding stuff to it, while allowing this kind of scenarios in an easier way.