Well, here's my take on the subject at hand. Many college graduates find it difficult to find jobs commensurate to their education because they majored in the soft sciences, humanities, and other liberal art fields where there are very little job openings. Jobs in the soft sciences, humanities, and other liberal arts fields are one in a million. Yes, it is easier to find a pin in a haystack than to find a job in the aforementioned fields. In order to find a job in such fields, one has to go beyond a mere Bachelor's Degree, one has to obtain at least a Master's Degree in order to find commensurate employment. Even then, many M.A. graduates in such areas still find it difficult to obtain commensurate employment. The best bet is to obtain a Doctorate in such areas if one wants to find a commensurate job.
Also, they have not networked with people who could get them such commensurate jobs. Many college graduates who have find commensurate jobs and even plum jobs have mastered the art of networking through summer jobs, internships, and family contacts. One does not acquire commensurate or plum jobs by being isolated. One has to know the art of networking and advertising one's self in order to be in the market. One has to be in areas where there is lots of exposure to the right people who can make things happen. For example, entering contests gains young people a lot of exposure which is beneficial as far as jobs go.
Their grades were merely hmmm average. Most employers want to hire graduates who have demonstrated a work ethic. The higher the GPA, the better as the graduates demonstrated a high degree of industriousness and diligence regarding his/her study habits. Graduates with an average or less than stellar GPA will find it extremely difficult to land a commensurate job as his/her work ethic will come into question. It is figured that if h/she did not fully apply himself/herself to his/her studies, how would h/she apply himself/herself to the job at hand.
Not presenting professionalism during the interview through demeanor, dress, and attitude. Graduates who obtain commensurate and plumb jobs demonstrate utmost professionalism in their demeanor, dress, and attitude. They WANT that job and they show it by their mindset, mentality, and psychology. They intend to have the interviewer take notice of them and the interviewer DOES.