You can argue on the other way round too by saying that why there is chettribad on security system. Why British Army and Singapore police have been dominated with Rai, Tamang (as you called it Gurkha) and why business is dominted by Newar? The work had been devided in such a way in multiple decades back. It is somehow continuing but remember in deminishing rate. It takes time to eliminate such system and may be in another coupple od decades you won't bee arguing in such a way as you are doing it now.