What are the reasons then?
I certainly can't think of any non Islamic cases where brothers etc have killed sisters to 'maintain the family honour'.
I feel that for a lot of self proclaimed 'feminists' it's just another justification to moan about men. They say "oh, it's all male violence" and then suddenly John the white, middle class, accountant from Kensington is responsible for FGM/honour/killings/etc simply because he's a man and it's male violence innit.
But if instead you look at it in terms of 'criminal' and 'non criminal' then a lot of the men you could previously lump in there and criticise are actually innocent. That's why these 'feminists' will often actively resist detailed analysis/profiling. Basically, all male violence is committed by men but not all men commit male violence. You may as well tell a catholic woman that's she's responsible for priests abusing young boys as it's 'catholic abuse'.
Those that like to reduce it to 'male violence' in order to berate John the white accountant will actively try and shut down discussion around the true demographic that perpetrate the crimes, because identifying the real culprits means they can no longer berate the innocent men around them.
These kind of behaviours are actually more harmful to the female victims than not doing anything at all, because they actively remove the focus from the perpetrators and onto men that aren't involved.