The wind speed on the top blade is significantly different from the wind speed on the bottom blades. This causes uneven forces. Uneven forces increase wear.

george e. smith gives a more technical explanation.

Because of the wind shear problem, the top blade (position) generates more torque, and axial thrust than the bottom blade (position). So the blades experience both a torsional and an axial oscillation at the rotation rate. So they literally shake themselves to bits.

I suppose in principle, you could feather the individual blades, as they rotate (even more bearings to wear out). BUT I believe that you can’t eliminate both the torsional and the axial thrust fluctuations at the same time.

If you change the angle of attack at the top of the circle to get the exact same torsional force as at the bottom of the circle in lower wind speed, then the axial thrust amplitude is even higher than without feathering, and if you vary the other way to keep the drag (axial thrust) constant over the circle, the amplitude of the torsional force is much higher.

So it’s a perfect nowin, nowin situation.

Well it is government supported. It doesn’t have to win to be profitable for some.