Hawaii is rabies free so any animals coming in usually have to go straight to quarantine. If they flew in cabin then passengers would be able to bypass this requirement and just walk off the plane and out the front door of the airport. Going cargo they're tagged to go straight to the quarantine facility. Besides Hawaii there are a few other countries that have the same requirements. England is the first that comes to mind. With some there are ways to get around the quarantine requirement but it's nearly impossible to get around the cargo thing. Here's a good link for Q & A from Hawaii's Department of Agriculture that might help you out. They're the ones that handle bringing pets into the state. Lots of good info.
Animal Quarantine Frequently Asked Questions — Hawaii Department of Agriculture