这个句子中肯定是用reason for. 因为my dissatisfaction只是一个名词短语.
最简洁的区别,你只需要记忆：
the reason for +短语
如：The reason for the change is lack of money.
the reason why + 从句
如：The reason why I beat you is that you do not obey the order.
俺是英语专业出身的,希望可以帮到你~