It is not at all a stupid question, quite the opposite. It is a very pertinent and also a complex question.

Unfortunately, I don't have the answer. There are myriad reasons and factors (from your biochemical makeup to your personal history etc etc) that could help shed a light on the 'why's'. And sometimes, it not even possible to find a satisfying 'why'.

This is something you would be best to explore in therapy - with someone who specialises in trauma for instance.