When you are looking for work as a freelance writer (or any kind of work for that matter), you need to present yourself in the best possible way if you are going to get hired. Have you ever looked at your writing resume and cover letter and considered the impression it makes on someone reading it for the first time?
Put yourself in the chair of the person reading your application and think about whether you are coming across like someone they would be interested in hiring. Have you explained who you are (a freelance writer extraordinaire, of course) who has the necessary skills and abilities to get the job done? Does the reader understand how your experience fits the project at hand?