I don't think it's a dumb question. Different people have different reasons.
As a few others have said, the choice of a DW didn't come about because of money constraints or not wanting to plan something big.
After attending a close friends traditional wedding together, we just decided the whole church thing with a lot of people wasn't for us. We love to travel, we got engaged on a beach, and we want a quiet and romantic ceremony. The big AHR is in place to celebrate with everybody who couldn't make it to the DW... and for me, a reason to wear my wedding dress again!
Also, getting married somewhere away from home gives our closest family and friends the opporunity to take a much needed vacation. And to all take that vacation together... well it's a once in a lifetime opportunity.