The person installing your application may not know anything about Java. They don't want a 35 page installation document. With a container, they just plug in

The person installing your application may not know anything about Java. They don't want a 35 page installation document. With a container, they just plug in your application and it runs. They don't know and don't care what technology it was developed with. You have complete control of your dependencies, which exact Java runtime you use, any other native libraries or tools you use, etc. They are all part of your container and independent of the host system. You can't see the host system, and the host system doesn't care what is in your container. The container is like a giant simple JAR file for any technology that runs on a Linux system. Once you know how to install and run a container, you can run apps developed in unfamiliar technologies. You don't have to know about their conventions for paths, or classpaths, or other things you don't care about. That is all packaged up inside the container.