The answer is that scientists don't like to use big numbers when they don't have to. So generally, scientists use whatever units are easiest for whatever they are working with. In radio astronomy, astronomers tend to use wavelengths or frequencies. The radio is a very broad part of the EM spectrum. Infrared astronomers also use wavelength to describe their part of the EM spectrum.
Optical astronomers use wavelengths as well.
Then we have the violet, blue, green, yellow, orange, and red light we know so well having wavelengths between 400 and 700 nanometers. This is a very tiny part of the EM spectrum. So scientists usually refer to these photons by their energies, which are measured in the tiny unit of electron volts. Electromagnetic radiation from space is unable to reach the surface of the Earth except at a very few wavelengths , such as the visible spectrum and radio frequencies . Astronomers can get above enough of the Earth's atmosphere to observe at some infrared wavelengths from mountain tops or by flying their telescopes in an aircraft.