This also assumes every pirate operates their own JumpShip. It's entirely possible, on some planets, for pirates to exist as a local nuisance; too large for the locals to deal with on their own but too small and localized for a larger military force to go out of their way to remove them. There's also the option for pirates to just buy a ride on (or hijack, if things get hairy) a legitimate transport JumpShip running its normal routes. I'm sure more than a few JumpShip captains are happy to take the money and not ask questions in some of the less busy regions of space, and even that aside the pirates could, with a little cunning, just pose as mercenaries on their way to or from a job.
Say, for instance, that you've got a pirate band consisting of a couple Intruder DropShips full of hired guns and three or four aerospace fighters. They hang around the system's recharge station or thereabouts, and extort tolls from passing cargo droppers. If the locals or feds get sick of them disrupting trade, they can lay low for a while, and try to find a JumpShip that hasn't seen the racket run (or simply doesn't care about the reputation of their passengers, so long as they pay up front and don't try anything funny while docked). Otherwise, they'll be able to run that con for quite a long time. When the jig is up as stated above, or freighters catch on and stop visiting the planet without plenty of guns of their own, move on to a system two or three jumps away (maybe taking some time to "borrow" some property on the intervening jumps), get yourself established with your leftover cash, and once you've got a feel for the place set up that same con again. If there is no option to escape the system any time soon, a planet is still a pretty big place. With even just a few members who's faces are relatively unknown, you can survive in the backwoods off of your accrued gains for anywhere from a few months to a few years until the heat dies down.
I suspect we don't hear about that type of piracy much because it generally doesn't make for too many intense stories about against-the-odds defenses or wild interstellar manhunts, much like how everyone likes to talk about Blackbeard and Bonne despite the fact that they represent an outlier in historical piracy. At the end of the day, it's a franchise about big stompy robots IN SPESS written by a variety of authors, some of whom may or may not have a habit of having at least one huge explosion every five pages and ending every engagement with a cheesy punchline. Credit to the authors that take the time to put a real focus on the more mundane, minor-annoyance aspects of the BT universe, for they're a relatively rare breed (at least in fluff; the crunch devs love their pointless minor details and it's great).
