Why did Wilbur and Orville test the glider from the ground first?

Before making free glides, the Wrights always tested their gliders by flying them as kites. Kiting provided valuable information on lift and drag, and enabled them to get a feel for the controls. The first year they built a tower with a rope-and-pulley suspension device to test the glider, but it didn’t prove useful and they soon returned to kiting.