I don't think he's super rich, but he's 63 and could probably live fairly comfortably for the rest of his life without working again.
Don't underestimate ego though. I keep thinking NG's peak fame as a writer was about 15 years ago. He's still famous, but he hasn't written a novel or graphic novel in years and mostly works as a showrunner for projects based on his old IPs.
It's not that different from how Spike Lee, who's been an old fart for ages, still wants to be the angry young man he was 40 years ago. Or these washed up actors who have barely worked in decades, who spend all day tweeting about politics and are sometimes rewarded with a Buzzfeed article saying "washed up actor from that show you kind of remember slams Trump".
I have ever more appreciation for the likes of Gene Hackman or Jack Nicholson, who retire and stay retired and don't feel they have to prove their relevance to anyone, and once in a while you see a social media post reminding you they're still alive. It's more dignified than a 60 something man wearing a leather jacket.