They can be. It's not necessarily the tool that's important, it's how you employ it.
When most people say "cardio", they mean a long, easy, low intensity session on a treadmill.
Short, hard, high intensity conditioning workouts are the best way to lose fat, and burpees can easily be integrated into such a workout, or even used on their own.
Try doing 100 as fast as you can. My best time so far is 6:50.