Because India didn't want an escalation after Balakot, and RoE for Indian CAPs probably were to scare Pakis away and not shoot them down, and Abhinandan's plane went too close to the retreating pakis. After they brought down IAF aircraft and took a PoW, and pakis managed to put down some munition on the Indian side; the paki side committed escalation. This is when many world powers sensed that a real war is brewing, because India was going to respond to PAF action with Navy action on Karachi, for the simple reason that Modi was provoked during elections. This was the backdrop under which Pompeo walked into de-escalation negotiations.
I'm sure India didn't bargain anywhere near as cheaply as "give us our PoW back, we'll de-escalate." India put itself in a position to ask for anything, like "move heaven and earth but get JeM on UNSC shitlist, and give us our PoW back, pronto." Even chicoms now admit their veto was only a technical halt and they will move forward on that very soon.