WIFI CALLING in INDIA

All major carriers both in USA and India allow wifi calling. I am not sure why AT&T blocked India for Wifi calling. I am an existing AT&T user planning to switch to a different network because of this issue. I like AT&T a lot but because of wifi calling option I have to move to a different carrier. I want to know if there is a genuine reason for AT&T to ban India from Wifi calling.