Despite being at war with literally everyone, having spaced-out colonies that can't safely trade with anywhere and all have resource deficits, and almost all their ships being scavenged wrecks that get mopped up by all but the smallest fleets, pirates are ubiquitous and keep people trapped in the core worlds.
If pirates couldn't sustain their constant losses of entire fleets and even colonies, they'd disappear. And they can't: They barely have any access to resources for building ships, and their battles definitely don't give them a net positive in ship count.
If someone or something wanted to keep the sector from recovering from the collapse, disrupting trade and stability in the core worlds and having elite fleets obliterate those roaming beyond would be the way to do it. Without ever being recognised as the real enemy, of course, so you don't get supermurdered by the entire sector.
