As much as candidates SAY they want the job, there are some who don't give off the impression that they really want it. And as I've noted many times before, it is critical you convey your excitement and strong qualifications for the opportunity you are pursuing.
Job seekers I've worked with recently have surprised me with their lack of preparation or effort in their job search. When you know you will be one of 10 or 20 or 100-plus applying or interviewing for a job, you must do everything you can do stand out in a good way, not a bad one. To convey you are the perfect fit, you should be very consistent in your message that ties your qualifications directly to the job requirements.