the answer here is map geometry more than anything(and a little bit about Viper). Icebox and Lotus are generally incompatible with flashes because they dont have "properly" flashable angles where you need to push an enemy off of, rather they have spots to clear more often than not. Thats why if you see any flashes on those maps its Skye played who couples with Viper to both clear and flash close (wall pop flashed)and deep pockets of the map and provide intel about said spots.