It gives you better control over your life. Cause that wife was utterly and absolutely dependent on husband. There was nothing she could do to improve her life if there were issues. And if he was gone (say due to being sick, dead, in prison) she was utterly absolutely effed. If be beat her up, she was helpless. If he was emotionally manipulative she was helpless. If the marriage just sucked, both were trapped. If he was feeling responsible, he would not leave her in poverty and would stay with her despite her being jerk too.
The kind of murder where husband kills wife used to be waaay more frequent then it is now. It is one of reasons for lower murders clearance rate ... cause these were super easy to solve.