"The same reason there are timed rounds, gloves to protect the hands, mouthpieces, etc.. "
My response, which amplifies yours, is that ALL SPORTS COMPETITIONS ARE CONTRIVED. The rules are made to establish the boundaries within which the competition takes place. This should be obvious, but in the "era of instant replay" we sometimes forget.
This is obviously true. My point is that if all these factors are equal, the larger (and therefore stronger) person will win the vast majority of the time.
You insist on comparing apples and oranges. When the only variable is size, the bigger man normally wins.