Why object if cheating by man(say polygyny) is more acceptable than (cheating woman) polyandry?

In the past the reason has been down to mommy's baby daddy's maybe - there is fear among men that they will be conned into putting a lifetime into another mans child. Women don't have have that fear because they know that the child is theirs, their main concern is having a male to provide "commitment" to her and her children, his being the biological parent or not to here, isnt that important.