This, and also the other Dragons haven't moved as long as Zeno. They have a whole life ahead of them. Zeno made the choice for them purely based on his emotions and own self. It's... hard to see him like this.
They already lost their minds technically. And you’re asking Zeno to sacrifice himself, AGAIN, for their sake. I think it’s okay for him to say “no. I don’t want to be the center of reincarnation anymore”
They don't have a whole life ahead of them though, they have a short lifespan and even if Zeno hadn't intervened, there were already signs that the end was close
Look. For someone who is immortal, I kinda understand Zeno's feeling to get an eternal rest. I also don't want the dragons to get hurt too. But I wish... I just wish Zeno let the other three dragons out and listen to their opinions first before he made a decision of ending their lives. I mean it's their life too. Maybe they might want to be sealed away or maybe they might want to die protecting Yona. We'll never know if we don't ask them