Design Monologue 27: The Powers That Be
Lest we forget; it is an easy thing to claim a square of land if you can defend its borders, but no so easy to claim the space inside a hollow sphere of star systems under your sovereignty. Whether your poison is FTL jumps, warp drive, or even jumpgates, the many parsecs between each system are just impossible to police without unfeasible IFTL (infinitely faster than light) hyper-accurate scanning devices to spot every ship violating your deadspace territory.
There is a tendency to assume that the original Homeworld empires are ever-expanding blobs, outlines on a map with colors telling you who's who. It would be quite inaccurate to label the immense space between even the most important core systems as being under anyone's political control.
Granted, the major powers do everything they can to monitor each system within their (often literal) sphere of influence. While FTL jumps can start and end anywhere, a pirate ship in deadspace isn't much of a threat. If one can keep them away from all possible resources (water, minerals, solar energy, etc), then they might as well be a million parsecs away.
Because of this, it is quite possible to pirate even the most secure systems, since one can easily hide outside the secure areas in deadspace until the time is right to strike.
In secure systems, most people travel by jumping directly from origin to destination. To get from planet A to planet B, you simply achieve high orbit above planet A, then jump into orbit of planet B, then descend. The whole process typically takes less than 45 minutes for civilian liner; military vessels can do it in 15.
Now, the number of satellites, stations, and ships in orbit of a civilized planet is such that no pirate would last 30 seconds. The speed at which a pirate would be intercepted in the control region of a secure planet is an order of magnitude greater than the fastest jump drive cycle times (measured in minutes).
Thus, pirates need a special opportunity. Often, they'll try to find the weakest link in a planet's defense grid, or exploit a temporary extenuating circumstance, such as a solar flare.
In a lower-security area, pirates have a much easier time. Generally, there are a small number of safe jump points; anyone who flies elsewhere is asking for trouble. Only a very densely-populated planet can support a true planetary defense grid, the rest have a few safe spots and a whole lot of unsafe ones.