Because you can rock it with anything really. You just throw a pair of jeans, a white shirt and some leather loafers and off you go. You can also be wearing your favourite suit with a pair of dress shoes and this jacket won´t make a dent on the attire.
Note: You can wear it all year. It´s probably going to be the best buy you ever did. Just ask Miss Palermo, if you don´t believe me.