I think people are just too used to Liberty.
In fact (It may be just me, 'cause I gotta have something agains weeaboos but...) I believe people like Kusari too much.
I've been playing a Neutral Trader for about a week now. Got myself a Train, wich allows about 3000 cargo, and with a swift route in and out of Rheinland I make about 17 mil in half an hour. This said route is made 75% inside Rheinland space, so I really don't believe trading routes are the problem.
Just my opinion but maybe people just don't like Rheinland way of RP. Take myself, for exemple, I just can't get used to saying "Heir" every five words. However, I see the Rheinland military an exemple to other houses, and I feel safer inside Rheinland space than any other.
On another side of the story, however, Liberty is crowded. I mean, crowded. There's simply no RP on, let's say, a Lane Hacker/Outcast literally camping just beside Fort Bush but that happens every now and then.
Just because you can doesn't mean you should.
An option would be to enforce defense in Liberty, which is the center of the game, and make economy more focused on importing than exporting. That would make pirates and newcomers spread towards the other houses, simply because there would be no action near on New York. Of course that assumes we'd be strangling the Liberty Rogues, Outcasts and Hackers, but if it is assumed that they can pirate that close to police bases, well, they'll find their ways.