Some probably has to do as blades/axis could break due to stress, which there are videos of turbines with malfunctioning brakes spinning out of control and brea

Some probably has to do as blades/axis could break due to stress, which there are videos of turbines with malfunctioning brakes spinning out of control and breaking. Mostly wind turbines have issues with frequency as you don't want to change/adjust frequency too much (adds to cost) to that of the main grid they only generate when within acceptable frequency ranges and internal equipment is able to compensate.