Why can't infrared remote sensing work all day?

Do you mean near infrared, middle infrared or far infrared? The working conditions of different wavelengths are different. Near infrared mainly reflects sunlight, and of course it can't work at night. Mid-infrared includes sunlight and ground objects' own radiation, which is generally used to detect high-temperature fires and can also work at night. Far infrared is the radiation emitted by the ground object itself, which can work all day.