Why does the vernal equinox block the sun more than the winter solstice?

Because the sun decreases from the equator to the north at the vernal equinox. After the winter solstice, the direct point of sunlight will gradually move northward.

The earth moves around the sun, and the sun always shines on the earth. The winter solstice solar term is the moment when the sun reaches the tropic of Capricorn, which is farthest from us. The sun shines at the largest angle on the earth. As the sun moves from the tropic of Capricorn to the north, the illumination angle will gradually decrease. By the vernal equinox, the sun has reached the equator, and the irradiance is getting smaller and smaller.