People only run CoF Explorable path 1 because it is incredibly short.
A simple solution to this problem is to scale the rewards of the dungeon based on how many times they are run by everyone. This would encourage people to do other dungeon paths for their rewards without rebalancing any of the dungeons or increasing the total amount of treasure given out.
For example, a dungeon path that has been run 100 times today would give less reward than a path that has been run 50 times today.
This dynamic balancing of rewards also encourages exploration of all the dungeon paths. The lesser done and longer paths would automatically become more profitable while the shortest, most often done would become less.