It's true that you can get to very low body fat without doing any cardio at all. Doing weights burns a fair old amount of calories, coupled with a good diet, you'll
look good.
But for me, health and fitness is about more than looking good. Doing cardio and having good cardiovascular fitness has more benefits than just fat burning. It is good for mental well being, it makes your body process food efficiently, you can do things physically that most people cant. It's awesome.
Plus, you get quite a lot of attention from women when you're out running, which is always nice