There's certainly no requirement to start using Docker images!
It's one of those things I would personally argue is a naughty hack that should be avoided if at all possible, but it's also something that's historically been ubiquitous within the Java ecosystem. It's frequently how convention-over-configuration dependency injection (as found in Spring Boot or Jersey) tends to be done, for example.
The reply I got on Stackoverflow from the person I think is the maintainer is "don't use fat jars", which is probably the correct solution, although most people use fat jars.
Lately, I've been reading that layered docker images should be a faster way to build and deploy java apps that have many tens of MB of dependencies that never change. It only works if you don't use fat jars.