Build tools like Maven provide excellent dependency management abilities. Of course Maven dictates a lot of how the build has to happen (source), but imho that is an argument against Maven and not against general automated dependency management.
The Github repository of IntelliJ is very confusing but I think they use Gant - which doesn't include dependency management, but integrates very well with Ivy. So I can understand why they might like using Gant - but why don't they use Ivy?
My actual question is therefore: what could be a reason the IntelliJ IDEA developers (or another team in another situation) didn't use a dependency management system and save their dependencies instead as normal jar files inside their repo?