As others have said, the problem is that there is an inherent risk associated with running any fossil fuel engine in an enclosed space attached to living quarters.
It's kinda like the Space Shuttle program. No matter how smart you are, no matter how well you plan......something can always go wrong. And when it does, it's catastrophic.
To clarify - I'm not a Predator, but one of my Generators IS
HarborFreight Predator 3500 Inverter