Please briefly explain the reason why Jinan Post Office chose the picture on the right as the Tomb Sweeping Day commemorative postmark.

China Post issued a set of three special "Qingming Festival" stamps on April 5, 2010. The contents include ancestor worship, outing, and willow planting. The face value is 1.20 yuan.

In order to cooperate with the issuance of the "Qingming Festival" stamps, the post office in Jinan, the provincial capital, has specially engraved a "Qingming Festival" commemorative postmark for use and collection by all walks of life. The commemorative postmark is a huge butterfly kite, with weeping willows fluttering in the wind, children swinging on swings and chrysanthemums embedded inside. The two characters "Qingming" are written in cursive script by the calligrapher Wang Xizhi.