I don't understand your first statement. You currently lose custody of your children by default, that's the problem. Attempts have been made to change the law in some states to fix that, but were defeated by NOW and their supporters. Currently, the law considers the best interests of the child to be "with the mother". It should consider the best interests of the child to be "with both parents".
A review of the cases does not support your claim. 8% of fathers demand custody because 8% of fathers feel the mother is so bad that the children are better off with the father. The fact that they generally win in such cases is expected, but can not be generalized to imply that if fathers simply seek custody more often, they will still get it that often. When they seek custody in cases where the mother is not abusive, they lose.
A review of the cases does not support your claim. 8% of fathers demand custody because 8% of fathers feel the mother is so bad that the children are better off with the father. The fact that they generally win in such cases is expected, but can not be generalized to imply that if fathers simply seek custody more often, they will still get it that often. When they seek custody in cases where the mother is not abusive, they lose.