One reason could be as Taashu mentioned, HR being not as lucrative as other career options. Also, now-a-days, more and more importance is boing given to the careers on the front end job profiles than the ones which are considered the back bone. Everything is getting showy. Thats why we have come up with so many job positions for for the same job descriptions. Taking a career plunge also depends on the personal interests of an individual. And there is no doubt that "money" plays a big role to decide its future.
Again, the career growth is another important aspect that cannot be missed on. Growth in HR is comparitively slower than most other functions.
So this could be the main resons that are pulling the crowd away from HR.
Never the less, let's hope for the best to come in times to come...