More understandable is the crime of passion, where love turns to extreme anger after finding you in bed with another or learning of your affair. No excuse but it seems a little better than a cold, calculated murder-for-profit. Better to be killed in passion than to be taken out like the trash.
People used to murder each other as the only means to escape a loveless marriage in an age where divorce was extremely difficult to get. Back then one could either kill the unwanted spouse or maybe hire someone to seduce him or her and get some damning evidence. Even so there was the stigma and the scandal. Far better, it must have seemed, to arrange an accident that gains public sympathy for your "mourning." As a divorced man or woman, too, you were damaged goods but as a tragic widow/widower you were a romantic figure indeed.
It may be small consolation to anyone facing the ordeal of divorce but it could always be worse.