I agree with you that it depends on the laws, but I don't think it is necessarily the case here. Would you consider the habbles to be more independent than the 50 states of America? Just because there are toll roads along major highways doesn't mean it is necessarily illegal to move things between states on local roads.
It actually does, depending on what "Things" we are talking about. Interstate commerce is closely watched and regulated, even if it's not to the level of national Customs, where politics get involved more. The most common example I hear about in RL today are people driving down to Southern states and buying cigarettes wholesale, then driving up to New York and selling them without paying all the state taxes on them.
Heck, if the ducts are established enough, goods that travel through such methods might be welcomed and taxed (taxes that would pay for the local exterminators). Paying taxes to 2 habbles might still be less than the tolls you accrue going through the 20 habbles in the middle.
That could makes sense, but doesnt seem to be the case here, or at least it's not a significant means of economic goods transport. Otherwise it would have been mentioned along with the toll-roads and the three outside Shipyards (though presumably there is some sort of controlled gate at the surface as well). I could easily see them piggy-backing water lines or vacuum tubes or Lift crystal Floats up air shafts or some such as an inter-habble Postal service, for example.
Consider also that the high cost of transportation might prevent certain goods from reaching some of the more out-of-the-way habbles. I would think that they would welcome any methods of getting more goods, and just make it legal out of necessity.
Why make it legal when you can Just Do It? That's precisely why these kinds of organizations form. Your argument is essentially "Why don't they just make everything people Want and Need Legal?" That's a spectacularly good question, but based on empirical evidence I think the answer is "Human Nature".