Why do we get tunnel vision during fight or flight response?

I have a question regarding tunnel vision during the fight or flight response. I believe that during fight or flight high levels of adrenaline are released which causes the pupils to dilate allowing more light to enter which allows us to be more aware of our surroundings. Why is it that sometimes we suffer from tunnel vision then? I know it allows us to focus on the main threat but if our pupils are dilated and more light is entering and hitting our retina how is it that we have tunnel vision? Shouldn’t we see more now with a dilated pupil?

Thank you for reading my question!