because sprinting is one of the best exercises to train the anaerobic system and any-time you use any explosive movement you are using the anaerobic system.
For a boxer to open up combinations at speed is using the anaerobic system, for a boxer to do sprint intervals would increase their ability to punch hard and fast, for how long they can punch, how quickly they recover to do it again.
The same would be true of any "explosive" movements in Judo that require you to use a lot of power.
On top of it training the anaerobic system sprinting will increase the strength of your muscles, tendons, it saturates your body with chemicals which allow your muscles to contract and release faster, it creates massive obliques and abs, and builds up the calves and legs a lot.
Sprinting will give you strength and endurance in your legs that will directly cross over into your ability to wrestle.
I said it before and I'll say it again, sprinting will also give you a clear idea of what muscular imbalances you have. If your quads and hamstrings have an imbalance you will notice, if your abs are weak compared to your legs you will notice, these weaknesses will scream out at you.
Not to mention how well a person functions during heavy exertion. If you sprint until you are pouring sweat, about to puke and pass out, about to black out, and you commonly do this, chances are your going to be fighting in situations where you are so gassed most people would be puking or passing out, you will recover from exertion super fast.
the idea that running only improves running is an ignorant idea.