I wonder the same thing. The only downside I can see is that the more days that go by while bug-hunting, the more anxious I'll get about not having a consistent biweekly paycheck. It would be a very results-driven career à la sales, but I'm not sure I could take that stress.

If you are legitimately good enough, there are certainly companies out there who will pay you well and consistently to hunt for bugs/vulns.