While it is true that not all Muslims are Islamists it is also abundantly clear that not all Islamists are Muslims.
Islam is a vehicle.
For the individual who needs a justification to satiate their lust for violence, Islam provides the God who condones the same. It is a vehicle which places the individual in the driver’s seat.
For the state which needs a deniable flank, Islam is also a vehicle. It is the vehicle which places the state in the driver’s seat with a large backseat of passengers.
Not all Islamists are Muslims. Islam provides the vehicle. The rest is blood sport.