Because it wasn't based on bloatware liks Electron. And I guess the developers actually cared about performance because at that time they couldn't just assume that everyone has a powerful machine.
Someone apparently isn't aware that IDEs can consume build scripts as project definitions.
I don't duplicate anything, my CI/CD pipelines consume MSBuild, Ant, Gradle, Maven, CMake, XCode, package.json, gulp, webpack files just as easy as my IDEs.