Reason #1 - Valuable Skills

The Law School Admission Council's Official Guide to U.S. Law Schools states:

While no single curricular path is the ideal preparation for law school, you should choose courses that sharpen analytical reasoning and writing skills. Law schools prefer students who can think, read, and write well, and who have some understanding of what shapes human experience.

The majority of the work you will do as a philosophy major will involve reading, analyzing, and presenting written summaries and critiques of arguments. These are precisely the skills you will use most as a law student, and later as an attorney. And law schools know this. Consider the following excerpt from American Bar Association's Council of Legal Education and Opportunity:

In assessing a prospective law student's educational qualifications, admissions committees generally consider the chosen curriculum, the grades earned, and the reputation of the colleges attended…Solid grades in courses such as logic, philosophy, and abstract mathematics are generally considered a plus…Law schools will respect your pursuit of subjects you find challenging. This is especially true if the courses you take are known to be more difficult, such as philosophy, engineering, and science. Also, look for courses that will strengthen the skills you need in law school. Classes that stress research and writing are excellent preparation for law school, as are courses that teach reasoning and analytical skills.

Reason #2 - Highest LSAT Scores

Many schools view the Law School Aptitude Test (LSAT) as the single best predictor of a student's success at law school. Your LSAT score will often play as great (if not greater) a role in determining your admission as your undergraduate GPA.

According to data provided by the Law School Admissions Council on LSAT scores from the past few decades, philosophy majors annually have the highest or close to the highest average LSAT scores. For example, the table below for the 2007-2008 exams shows philosophy majors had the highest average LSAT scores among the twelve most popular pre-law majors, tied with economics.

NOTE: For major fields with at least 1,900 students taking the exam.
Source: Niaswiadomy, Michael "LSAT Scores of Economics Majors: The 2008-2009 Class Update," Journal of Economic Education, Vol 41(3) July-September 2010:331-333

Reason #3 -  One of the Highest Law School Admission Rates

According to National Jurist, philosophy majors are admited to law School at a higher percentage than any other major.

Source: http://www.nationaljurist.com/prelaw/classics-philosophy-majors-do-best-...