Comment by antonvs

This is just a testament to how widely Java is used, and in how many different ways. Sounds like you're more focused on "Core Java" applications, or something like that. Every company I've been with since the late 90s was using application servers of some kind until Docker came along. And all of the more recent ones switched to containers and ditched the application servers.

The switch was often much more than a minor upgrade, because it often made splitting up monoliths possible in ways that the Java ecosystem itself didn't have good support for.