War, bad condition and cannot leave women alone. One of the few reasons but not the main. Let me put an example in front of you. For example, if there is couple who are having trouble having kids. Should the wife, family and society give the husband to marry the second time, knowing that he can have kids?
I know that there are individuals who abuse this practice. They are many practices that are abused and misinterpreted. There has to be proper channel of knowledge of society in general about this issues, but again I will ask why is it a big no no?