That's the point. If they were doing their job and interrogating well as well as investigating well they'd catch them all just like Sabu. Unfortunately they're not and it's easier to offer a plea deal after a short period of intimidation so they do that. I think they should all pay, but this way they just abuse something built into the system that was made as an incentive for people they didn't think they COULD catch otherwise.
With Sabu, they caught him on mere chance. He connected directly to IRC from his home address, without proxies or going to a wifi hotspot to hide himself. Not everyone will make that mistake, and then it becomes infinitely harder to find them. It's about resource management.
> If they were doing their job and interrogating well
> as well as investigating well they'd catch them all
> just like Sabu.
They used the fact that Sabu had their trust. The idea that they would be able to plant someone in LulzSec and take then down from the insider within 7 months seems laughable.