Ironically, this king was the one exception that was benevolent and fair. The knight, of course, was a member of MAGA - Make Arcadia Great Again.

One of the reasons I can never stomach Nick Bostrom's Fable of the Dragon Tyrant because it depicts the idea of a stoic king who cares about his people.

(Also, glosses over completely how an ageless soceity would be stacked under feudal-capitalism)

Many powerful people like to make people believe (and possibly believe themselves) that they're just rulers. And it's just plainly more effective when your underlings are well-informed of your intentions (assuming you're not trying to set them up). e.g. imagine if the knight thinks that a dragon is a direct threat to the king and burns down the countryside to hunt it (any means necessary etc.), when in reality it's not a direct threat to the king at all and you were just supposed to keep the countryside safe from dragonfire.

Of course, the entire premise is that it's not obvious to the knight why a dragon must be killed and what are acceptable means to achieve that. e.g. in Faerun's Sword Coast, you'd expect that every knight is well-informed about this.