Containerizing Java applications is not a trivial task and also there is a learning curve involved as you have to get yourself familiar with tool-specific commands etc.

I can say from personal experience that not all Java developers are container experts.

For example, first, you should have docker installed and then you have to maintain a Dockerfile. Then over a period of time, the image size grows and you start trying things like multi-stage builds to reduce your image size and have only required dependency for your application.

A developer ideally should not be worrying about these things. With Jib, you don't deal with such complexities and you just have to add a plugin to your build tool Maven or Gradle and you are good to go. It takes care of your image building and pushing to the container registry.