During tough economic times job interviews are difficult to land, and some of them more so than others depending on the industry that interests you. Your cover letter must show who you are as a person, as well as a professional.
The interviewer asks: Why has it taken you so long to find a job?
It’s difficult to believe that employers are still asking this type of question. Don’t they read the newspapers or listen to the news? If they were informed, they would know the answer; i.e. jobs are very scarce and difficult to find these days, and unemployment is still high, despite improvements in the economic picture.