I think you have your answer:
Well, I got 50 applicants. Out of 50 only 3 put 'sunshine' and all of them turned to be not as qualified as I wanted them to be.
While this "trick" seems thoughtful in terms of being designed to focus on detail-oriented candidates, it's also way outside the norms of typical hiring processes, and as such you may very well be losing a lot of very well qualified candidates. And, based on your results, it's not exactly filtering the list down to people you actually care to interview.
Ask yourself this:
Would you rather lose a few otherwise perfect candidates because they forgot "sunshine," or would you rather not waste time filtering candidates yourself?
Trick aside, you really need to do the important work: review your hiring process and make sure your requirements and your benefits are in line with the industry in your region, and - assuming you don't find some smoking gun explaining the lack of applicants, ditch the sunshine thing because it's clearly not working.