I think it was just a lack of care. He wasn't interested in how shooting Dick in the head effected Dick's character. It was only there to serve Bruce's ongoing story and King tossed the character back to the Bat office to deal with after shooting him. King was going to shoot Dick regardless of what anyone thought and just told the editorial office that if they didn't like it he he could have Zatanna show up and undo it so the Nightwing book doesn't get impacted by it. That was the extent of King's involvement in the Dick side of the story. They decided to run with it for the boost in sales but it has been managed horribly. At the end of the day I just don't think King cared. If he actually cared I don't think he would have shot Dick in the head and then not care what was done with it afterwards. He would have had a story lined up for it.
I lost a ton of respect for King as a writer when he did that. Morrison or Snyder didn't do that in their runs from what I remember. Given how the Grayson book came about after Johns threw Dick's character under the bus the same way in Forever Evil when he exposed Dick's ID to the world with no plan to follow up on it screwing over Higgins' run, you think King would have known better since he wrote Grayson.
I think he said that only while he was writing Grayson. You see a lot of writers say that when they are writing a character to endear themselves to their fanbase. I mean I think he is a fan of the character but I don't think he is a character King has much interest in anymore. He wrote his Grayson series and is more interested in other characters.