Not sure why you wouldn't want that liability insurance, all that has to happen is a fuel leak sourced from your vehicle that leads to a fire that burns down one or two 737s on the stand and you might be looking pretty shaky without it. Liability has nothing to do with what your asset is worth, its what the possible damage to other assets that could occur or injuries, airports have some pretty big ticket items floating around, I would want a minimum of $20mil liability insurance personally. The reason why some airports require it is that they don't want some poor bastard in his $2 Cessna not being able to pay for damage they caused.