because of the GUI. I'm sure that 90% users do not want to go to an website, config their layout, copy to an other website to make some .hex file then using command line to remap their keyboard.
What users want is this: Clone a GIT repo, install few dependencies via Brew, change keymap in C file, compile and download hex file to board !
No fiddling with silly GUIs that need specific operating system, probably, windows only.