Is it because the code uses delayMicroseconds it is actually working like a pwm and the voltage just is not enough to trigger the driver?
No. It is hard to tell just what you are measuring in that picture, but the meter reading shows 3.19, which, for a 3.3V board, is reasonable.
With nothing connected to the Arduino, what do you measure at pin 8?
What, exactly, is connected to pin 8?
What is connected to what other pins?