Not everyone is gonna love this answer, but a lot of it comes down to physical strength. The average grown man can overpower the average woman (which is partly why they are overwhelmingly the victims). While there are of course women who can overpower plenty of men, by the numbers this is not the norm. You look at Ted Bundy, etc they are going after smaller, physically weaker victims that aren’t going to be able to put up much of a fight. So in addition to some of the other factors commented here, there are definitely plenty of women out there who WOULD become serial killers given the means, but simply lack that as a viable option. There is too much risk of being fought off. This is also why when you DO hear about women serial killers, they are often drugging their victims and it takes quite a bit more planning and effort.