Optical Cameras need light. We normally get that from the sun.
The sun goes away at night. Thus we need artificial illumination.
If we want light humans can see, we use a normal light. But if we want light that doesn't distract humans, we use infrared, which humans cannot see but cameras can.
The IR we use is right near the visible spectrum. The IR you mean by heat is far infrared, which requires completely different cameras due to drastically different wavelengths. It also doesn't let you do things like see if you're looking at a phone.
Functionally, the driver camera in older cars cannot see you at night, as it has no reliable light source to illuminate your face.