That just happens to be when comets are typically most visible.
To give a little more context. The tail is created by the solar wind, and is strongest when the comet is closest to the sun. Being near the sun makes it appear close to the sun in the sky (obviously). That puts comets in the daytime sky and impossible to see. It only dawn and dusk when you're still able to see in the right direction and the sky is dim enough that you are able to observe comets.