I think the motivation for hardcore players to raid every night is both progression and gear.
If it was not so they would stop raiding after the first successfull complete run.
They keep raiding to have at all times the best in slot gear. Even loving the game, there is no one that doesn't at one moment get bored of doing the same things night after night for 5 months, even more if the gain is so low. I saw that happening on WOW.
According to some calculation I saw, the dps gain on a mercenary with full Dread Guard gear when compared with full Campaign was around 2%. What kind of incentive is that to continue playing?