Let's not discount the internal politics of dealing with Verstappen. They are clearly at odds with eachother and Ricciardo probably doesn't want to have to fight to be the number one driver on a team.
Hulkenberg is a solid driver, but I'm sure Ricciardo negotiated to be the no-question primary driver at Renault. And it's totally deserving, Ricciardo is an amazing driver, probably the cleanest overtaker in F1, and a genuinely likable guy. Outside of Verstappen I'd be surprised if another driver had anything negative to say about him.
Red Bull done fucked up.