|You may or may not be doing something wrong, while the applicants who made appointments and failed to keep them are definitely doing something wrong. |
Part of the problem is that although there are many serious jobseekers, there are others who are actually job-peekers. They like to test their marketability and even their interviewing skills, so they go through the charade of applying for a job and think nothing of ignoring interview appointments. This is more likely to occur with applicants whose expertise is in great demand.
However, other factors may be causing the problem. For example, perhaps the applicants do not like what you are telling them about the job or company, or maybe issues as basic as the pay or benefits are turning them away.
Just as you are interviewing applicants, remember they are interviewing you. Perhaps you should do a practice interview with one or two of your employees and see what kind of feedback they give you. In addition, while you could send reminders by phone call or email, do you really want employees who need to be reminded about a job interview?