It's only because your Wind force field is oriented in the exact same direction of your cloth planes. Just rotate the force field a little bit on Z and it will work.
Also, I recommend you to use the noise setting of the force field, as well as animating the force field rotations with some noise modifiers on its curves. It's not needed, but it might just add a little more appeal to your animation.
Just set the field force to 100000 strength and see then what happens. The default strength of 1 does nothing.
The other thing is weight of the cloth against the wind strength. If they are in balance, the cloth will be flapping more.