Because it's cheaper. Disney has made a mistake in how they charge for an AP on the payment plan. Do the math:
$269 - $87 = $182 $182 divided by 12 months = $15.66666.... which is rounded off to $15.17.
There's only one problem with this: You don't make 12 payments. You only make eleven! On the day you buy the pass, you pay a down payment of $87 and that is all. You don't make a payment on the balance until the next month. That means a $269 SoCal pass only costs you $253.83. Do the math with all the other passes. This means that the $649 Premium AP actually costs only $602.16. If you bought five passes at this price, you would save $234.40.
I was wondering whether I should write this thread because it's possible that Disney would learn from it and make changes, so keep this a secret, okay?