Because Rosoboronexport pays them to.
Given the "performance" of Tunguska, Igla, Pantsir, Buk, S-300 and S-400 against repurposed Neptunes, cruise missiles, guided missiles, JDAMs, military drones, civilian drones and repurposed flying dustbins (Tu-141) I wouldn't put too much faith in the ability to intercept anything barreling down towards my command bunker at mach 15+.