Why can't you have sail-powered airplanes?
High performance sailboats can sail faster than wind speed in certain conditions. Therefore, your question is not as absurd as it might seem at first glance.
However, the technique that enables sailboats to do so is not available to airplanes, at least not in flight. Sailboats use the speed difference between water and wind. Their keel keeps them from being blown with the wind. A glider in the air has no such second medium to resist being blown away by the wind.
Historically, the Andrée ballon used for artic exploration in 1897 tried to &quot;sail&quot; by combining sails and trailing ropes. However, this did not work in practice.
The only way to extract energy from the wind is when this wind changes. Wind gradients allow albatrosses to soar dynamically, and changing updrafts can be exploited by changing the load factor.