Greg responds...

1. It's complicated. There isn't one single reason, one single event. It's cumulative. It involves things that took place over the five year gap (SPOILER REQUEST. NO COMMENT.), his relationship with Artemis and his general maturing as a human being. A choice to leave behind things that seemed extremely important to him as a child - and not so important as an adult. Also, keep in mind, Wally didn't decide to stop being a hero. Wally and Artemis together decided to stop being heroes.

2. Nightwing wants what's best for his friend. I'm not saying they didn't have a conversation or two. Or six. Or whatever, but...