It is actually sand, which turns the entire phenomenon hot. Sand cannot hold the heat. It acts like a mirror to the sun. During the daytime, it stays warm, and when the Sun is absent it loses all its heat making the nights colder. There’s nothing in the desert that can either absorb heat from the sun or hold it on the surface when the sun is set.
The Sun in the desert can reach the zenith due to which the temperature rises up to 100 degrees Fahrenheit during the day. The sand in the desert gets heated up due to this high temperature, but it continues as long as the Sun is high up there. As sand cannot hold the heat for long, it gets cooler as soon as the sun sets.
Summer nights might be little warm but winter nights have temperatures below the freezing point. The heat from the sky gets radiated into space and hence the temperatures plummet to nearly 40 degrees Fahrenheit during night times. The desert animals and reptiles come out during night times.
When it comes to normal places, it is the water vapour and carbon-di-oxide present in the atmosphere that keeps our nights warm. As there are no trees and water in the deserts, there is no source of these to keep the temperature warm.