I'll tell you why. It's because they lie.
They put the car in as a customer order, use either someone on their staff or an employees' friend, family, to "fake" it as a customer-sold order, and when it gets to the dealership HallelujahMOTHERMARYJESUSANDJOSEPH! the order "falls through" on some technicality BS, and PRESTO! Hellcat on the showroom floor. With a markup!
Meanwhile, genuine customer orders are still not delivered. Hell, some of our guys in our local club don't have freaking VINs, despite having orders in on the day order banks opened.
Meanwhile, FCA starts posting "here's how allocation works" blog entries and news stories, and blaming dealerships who have tons of orders in, because most of those dealers are ones selling @ MSRP (or close to), and everyone on the forums / internet is flocking to those dealerships that actually order and sell the car to enthusiasts without markups.
As long as the allocation system favors volume dealers / sales in any way, shape, or form, it's destined to fail.
If FCA was serious about getting these cars into the hands of their loyal, enthusiastic customer base, they'd find a way to do it.