Daggers are by definition double-edged. Push daggers are a special type of dagger with a horizontal hilt allowing the user to punch with it. Specifically, punch through ribs. Blades are typically short around 3". Knife fighting requires a lot of training, and can be dangerous. Push daggers however are more instinctive - everyone knows how to punch.

But a double-edged blade has been the rule for weapons since the bronze age. They maximize the utility of the blade to a variety of combat scenarios.

I was arrested for having a 3" push dagger in CT 20 years ago.