When candidates are hired, HR is done with them (from an applicant standpoint). Of course, this is a very great thing because the process was a raving success and we can move on to the next recruitment. Unless we work closely with them as an employee, we are done knowing about their skills.
This is where rejected candidates come into play. They have to work harder for it. They are working to find out why they weren't a fit, whether we might have something else for them, etc. I get to know these people in a way. Because their continued interest is so unusual, I remember them.
There have been a few of these candidates who have gone on to be hired. Some I have actually recommended. Not for hire of course but for consideration.
Is it a big surprise that these eventual employees are often the best employees we have?
In fact, I was once one of these rejected candidates. Let that be a lesson...