why in still not an option to stop wifi for applications like cellular data
WiFi cannot be stopped for application same as for cellular data
There is no option to selectively choose which apps use Wifi if it is turned or not. If you need to temporarily stop Wifi, you can swipe down from the top right hand corner of your iPhone to open Control Center and tap Wifi, which will temporarily turn it off. Or you can go into Settings > Wifi to completely turn Wifi off.