That is because more Gurkhas serve in the Indian military & paramilitaries than the Royal Army or even their own army(which uses Indian weapons like the INSAS).
Well man our own army also has name which is "THE ROYAL NEPALESE ARMY" and we use weapons like M16, M4, INSAS, SLR, GPMG, LMG, SMG, Minimi etc and ofcourse our traditional and best weapon "KHUKURI" well it is not khukri or kukri it is
KHU-KU-IR.