I wonder if they're not more concerned with the balance of the trailer if you use that as a patio. If you have 3-4 people back there in addition to a heavy bike/atv, etc, perhaps it could tip back? Talk about taking a ride! These 'super lite' trailers aren't as tongue-heavy as what you normally see in models with the patio option.
3-4 people could weigh up to 1000lbs (thinking Wisconsin, here). That's a lot of negative tongue weight leverage... At the very least, they'd need to add better/stronger rear stabilizers, and that costs money. The factory stabilizers are barely adequate for the trailer as it is, and that's being generous.
If you're smart and factor this into your modification, you'll be fine, but the company has to design for the 'lowest common denominator' customer.
So: Jayco wants to avoid a lawsuit. That's my guess as to why it's not an official option. *shrugs*