It's not that hard to understand.
When you come to raid, her chief goal is to prevent you. The best way to do that is to make you fight her *AND* the council at the same time. If you want her to fight you without the council on her side, then you need to make it worth her while. Kostyan does this well. He'll come alone, and say something like, "Come out and fight me, or I'm calling in the rest of the cabal." The defender then has to decide whether he's more likely to die against Kostyan alone *without* the help of his cabal inner, or against Kostyan+friends *with* the help of his cabal inner.
As for why he wouldn't come retrieve- he doesn't have location object, so he can't tell if you're online. You have insects, quicksand and earthbind. That translates to a high probability of death.