Seem to remember ,not sure if it was here,where the tourists areas and tourists were warned and there was still a huge loss in those numbers. A warning to the masses would have been chaos as most in the poorer low laying areas would have had no means to evacuate.
If you recall the images from florida keys when a Hurricane is coming ,the lines of cars trying to leave ,now imagine if it were a Tsunami hitting within several hours of a warning.An Asian warning would be absolutely freaking moot in saving lives as most wouldn't even have vehicles . ,IMO.