Don't know if anyone really knows for sure, but I think it's because of all the variability of the climate. They know for a fact that virus dies at quick reduction at 56 C. Pretty hot, but I don't think they can say if regular 30 C or below with fair humidity climate can effectivly kill the virus on every surface. In other words, it might survive on a car door handle when it might not survive inside the car. Too many variables to say for sure, but we still have to roll, don't we?