Is there a scientific reason why there are no 325 lb.-525 lb. male bobsledders?

I could cite the low hanging fruit reason why, but I entertain there might be something less obvious as to why there are no bobsledders 325 lb. and up. I would think their added weight would be a plus to the sled, gravity and all. I have seen some ”beefy” bobsledders but none tipping the scales near 325 ib. or more that I know of. Other than not having the desire to hurl down an ice chute at 70 mph is there any scientific reason at all that would preclude a man that larger from being on a bobsled team and moreover, being an asset to the sled?