It's a logistical issue in Rheinland really. New Berlin is Rheinland's hub in many ways, not only because of the Diamond/Niobium run, but mostly because of the Sigma-13 jump hole. I promise I'll write a petition to put a minefield around that place anytime soon.
That hole is the backdoor to Rheinland and not only it sits a couple of dozen clicks from the capital, there's a trade lane right next to it. It's insane. Not all times, but we do try and do round patrols in all Rheinland systems if we get the chance (mostly for a change of scenery to be honest), but it's not uncommon to get to Hamburg or Dresden just to be called back to New Berlin because there's **** hitting the fan outside the capital.
Strategically, what we do ends up being the best measure to keep New Berlin (and Rheinland for that matter) safe. On the lines of what you've said, I suggest we do random patrols more often, something we already do from time to time to great effect (I believe the majority of the smugglers we've caught were passing by either the Bonn or the Brandenburg crossing).
Statistically, most of the trouble ends up going to New Berlin anyway. However, now that the RFP is getting on its feet again, I'm sure they'll be of great help to us spreading up a bit.
Practically, we don't have a lot of other possibilities for checkpoints other than New Berlin. An excellent strategical spot for our forces to place a checkpoint would be at the Essen/Dortmund crossing, given it's proximity to New Berlin and the fact that it is an alternate route to that of the Planet, but that place is so heavily and constantly hit by Hessian NPC patrols it's hard to pay attention to what's passing by since you're most likely fending them off.
Pirna is constantly hit by Hessians and the Wild, not to mention there isn't much in Dresden and we try and avoid to move too close to Vogtland, so the Hessians have at least one safe haven inside of Rheinland.
The number of Hessian NPCs at Manheim is insane, it's impossible to stay there. Mainz is a bit better. But then again, who comes from Sigma-13 through Frankfurt when there's a faster way directly to New Berlin anyway?
Planet Stuttgart and the whole system is somewhat peaceful, but most of what comes from there is Nyobium to the Ring.
Even though there's a lot at stake in Hamburg in RP (the prison and the shipyard AND the borders to Liberty) there isn't a lot of activity there. When the [W]s were around we used to spend a lot of time there. Still, if I was to say, that's the second more frequented system for us.
Another issue is that RM can't afford spreading out too thin, since we almost exclusively fly fighters. We have to rely on each other for protection and firepower, so we can't really afford to be too separated from each other should some problem arise.
Also, you have a lot less freedom when you're playing law enforcement. We have to worry about numerous things (civilian protection, law enforcement, smuggling and piracy disruption, direct attacks against ourselves, civilian unrest and territory). Not only we pack up for protection and strength, but we end up packing up to configure a processing unity capable of addressing all that.