Why does Spring Boot generates a jar?

Why does Spring Boot generates a jar file output, since a jar could not be deployed to a container or an application server?

It's nice to get it quickly set up (with an embedded container), but eventually you will have to build a war file in order to deploy the application properly.

Furthermore, it is a good choice to stick with spring boot also when the project is in production? From my point of view spring boot is just as a quick way to get started, but I'm not sure about it's reliability.