A lot of commenters referred to money being the biggest driver but I think that's only a half truth. Rather, job security seems to be the most logical reason to study computer science. No matter who you talk to, in any field, there's a huge consensus that having knowledge and experience with computers increase your employment prospects (I'm sure this could be proved by scanning job boards). Combined with the current job market and popular opinion that college may not be worth it (especially for non-STEM majors), I'm not the least bit surprised that CS has gained such an enrollment.