Why doesn't Tomb-Sweeping Day use the lunar calendar?

The traditional festivals in China are based on the lunar calendar, that is, the "lunar calendar".

But Tomb-Sweeping Day is an exception, because Tomb-Sweeping Day belongs to one of the 24 solar terms, which are used to arrange farming and celebrate leisure during festivals. Obviously, solar terms are more important than festivals.

Twenty-four solar terms are based on the angle of the sun in the sky, that is, the solar calendar, the so-called "solar calendar", from which farmland farming and other activities are arranged. Solar terms are most closely related to the Gregorian calendar, but mainly depends on the sun, so Qingming is always in those three days.