Herding by Ivy Leaguers into consulting and finance can be explained by three factors:
Starting Compensation, Future Compensation Potential, and Status of Profession.
Does this negate your argument? Probably not. Does not change the probability an Ivy Leaguer will choose to work for a non-profit.
But then again if you have amassed the most debt of all college students, you want the professions which make it easier to pay off your debt.
Call it then a vicious cycle or whatever you will, but there exists the distinct possibility entry into the two professions is not mindless herding but constrained choice.