Simon's taking inspiration from George R R Martin - introduce a character, get people to like them, kill them off unexpectedly.
No, get people to talk about them than kill another one off.
"WTF George why did you kill another Stark?" (Red Wedding - Rob and Talisa)
"Oh come on dude, seriously stop killing off Starks please" (Red Wedding - Catelyn)
"Ok, I'm going to shut up now in case you kill another. BTW, when is Book 6 coming out.. WTF you just killed off Jon Snow you bastard."