One reason: because you can afford it (or at least your parents can). The reality is that a diploma from a Ivy League school is an E-Ticket to certain things. It's not fair, but very little in life is "fair".
Harvard is a rip-off -- it offers very little except admission to an elite club.
Admission to that "club" is also admission to a network of contacts that can be leveraged for years after you graduate. Is it worth it? Depends on what you do with it.
The point I was trying to make is that people pay $250,000 and don't get any kind of special education. Harvard doesn't give them anything except an E-ticket.
Again: it might be worth it. But that's price gouging. At some point, society might wake up and say "You're really just like everyone else. Your resume doesn't actually impress me. Tell me why you're really special."
And the Ivy League grads will stare and have little more to say than: "Did you read my resume??? I went to Harvard!!!"