When an applicant goes into their system, they might not recall that they've already signed up for an account previously. So, naturally, they click on the sign up button. Then, if they add in an email address that IS ALREADY BEING USED IN AN EXISTING ACCOUNT, they STILL get a success message...it's confusing ... it says:

Great! You have successfully signed up for an account. However, we need to confirm your account before you can log into the system. Please check your email for a link to confirm your account.

However, since they already signed up previously and already have an existing account, the email never comes.