Seriously, as a mostly C++/python/R developer, maven was a PITA to set up for experimenting with Java, and I still don't feel like I entirely understand the npm/bower/yarn ecosystem. (Will they install globally or locally? What permissions do I need? etc. etc.)
It's certainly not something that I can't learn, or something that's really all that complex, but it's another barrier to just messing around with a new project. It's better for the frequent-users than the infrequent.
As an infrequent user of Java/Javascript, I'm fine with just downloading a tarball or cloning a single all-inclusive repo, and dealing with it being harder to update or to push a change back to the source project.
Even in python, I just maintain a local global install and occasionally update numpy/scipy manually. I'm not saying it's the best setup, but it's pretty easy to download verson X.Y.Z, config/make/make install, and done.