Why? Well, here's a few reasons.
Instead of the usual bright shiny balloon and free hot dog big tent sale buy it NOW marketing of most cars in America, you have the chance to order EXACTLY what you want and know, up front, EXACTLY what you will pay for it. Yes, the price may change slightly if you order in one model year and take delivery in the next model year, but still you'll get EXACTLY what you ordered and only be expected to pay the price you accepted.
Sure, if you want to fall victim to the old buying model you can run down to your local smartcenter and over-pay for options you don't really want or need. If that system works for you, then go for it.
For those of us that "get" the concept, we're perfectly happy to fidget out the wait and get the THE cars we want.
I'm sorry you don't get the concept. Go buy a Yaris, a Fit or a Ford.