You also dont see warning labels in your car not to run the engine in an enclosed space due to exhaust fumes, or a label on your toaster warnign you not to take a bath with it. Most hotels aren't explicit in every detail of what is against their fire prevention rules unless asked as otherwise there would be signs on everything, that would still be ignored (people wondering why their croissant caught fire when they ignore the signs to not put them in the toaster). Most hotels do not allow guests to use candles or incense in the rooms, and all of them that have electric heaters all ban putting clothes on them due to the fire risk.