Why do colleges care about extracurricular activities?

Bryan Caplan asks:

Colleges care about applicants' extracurricular activities.  Employers don't.  What's going on?  I'm tempted to just repeat my adage that, "Non-profits are crazy," but even non-profit employers don't seem very concerned about how you spend your spare time. 

Theories?

I'll take the bait.  Colleges want to expand the heterogeneity of the selection criteria so they can pick who they want.  If it's a top college or university, mostly this means limiting the number of Asians and maximizing the number of future donors and by the way those two goals tend to move in tandem.  Other than legacy admissions, I wonder what other features of applications predict future donations?  Might extra-curricular activities be one candidate here?