It’s important to note that potential power increases with the cube of velocity, but too much power means the forces are so high that it’s impossible to keep the system from self destructing.

So the curve plateaus because the turbines purposefully puts on the brakes to limit power. And at some point the wind will be so strong that the turbine is completely shut down.

If a turbine were capable of operating at full power under 100km/hr winds, the output would be spectacular.