Nothing is more frustrating than discovering that you need to install a new component or build system just to build a specific component. It gets worse when dealing with multiple external components in different build systems.

"It's also very hard to learn and very difficult to maintain"

I agree insofar as most people go into make without trying to learn it properly. There's a manpage and pretty good documentation for the GNU extensions. But in my experience, with custom build setups using stuff like Maven, a lot of time is spent fighting the build system when a simple Makefile would suffice.

"with the added benefit of not having to learn a new language."

You've shifted the burden from "learning a new but very simple language" to "learning a framework atop your language", which (based on my reading of gradle's docs) is not very concise.