It has been studied (and continues to be studied). There is even a term for people who kill their whole families, they are called family annihilators. Often times, they are people who are well-respected and have a high opinion of themselves (whether or not they deserve it) and when something threatens that sense of self, they kill their families rather than themselves. It's very interesting, although, yes, extremely sad. I don't think it's necessarily becoming more common, I think it's more a matter of these things getting a) traced to the perpetrators through forensics and b) more widely publicized on a national level.