There's an odd proclivity of developers of build tools to assume that their favorite runtime (be it python for scons, etc) is already available or trivial to nicely install. And that's just... not true.
The build tool itself is the one place in the ecosystem of building software that we have the least room for manual dependency handling and manual setup, because there's nowhere left to punt the hard part.
Make isn't better at this either, but it's been so widely packaged and is so nearly-default available (it's remarkably hard to get a working desktop system without some transitive dependency having gotten make installed for you) that it defacto gets a free pass on this.
My hypothesis is that these newer build tools would have a much better shot at reaching adoption if they were well-packaged enough that a single tarball (with zero external deps) or a single-line install script (think: "gradlew", though even that was cheating by assuming an existing jvm) could bootstrap them. Most don't seem to have invested that effort. And it shows.