First of all, let me tell you how many bankers exist. Its innumerable. So given the large population of financiers, this is a relatively low number of suicide.
Conspiracy theorists would like to make something of it, but obviously there is no secret issue linking these deaths. It's likely due to the stress level in finance. Trading is extremely stressful, when I say extremely..you probably cannot fathom what it's like to work every day under that type of pressure. It's also a highly competitive environment, where a single misstep personally or professionally can ruin your reputation and career. Finance guys are judged by their peers and superiors on everything from the age of their wives, to length of marriage, gpa, graduate school, place of birth, dog choice, I mean literally everything because in their world they analyze everything to death - literally as you can see.
Yup, nothing to see here folks. Go back to sleep.