After the ending, the Hero (and his bloodline) basically ends up ruling over half of the world anyway.
This only applies to the original Famicom version of Dragon Quest I. You know why the Dragonlord's Superdragon suddenly attacks you after you killed the Big Bad? You just killed its master and it is really angry about his master's death.
I'm very curious as to where this rumor came from. It's refenced in as least three tropes on the main page, and it just isn't the case at all. After defeating the original Famicom Dragonlord ("Ryuuou"), three words appear, meaning "Dragonlord," "true form," and "revealed." Then the dragon appears, with the same "Ryuuou" name. What's up with this?
The Explorer's Handbook that came with the US NES game gives a (false) origin story for the Dragonlord in which he was a hermit living in the Mountain Cave who, when exploring the depths of his home, stumbles upon the superdragon, and is surprised when it kneels before him. (This was presumedly to hide the final battle's reveal, as the rest of the handbook is a walkthrough that doesn't cover the second half of the battle.) It then erroneously states that he stole the Ball of Light and Princess Gwaelin in two seperate raids, with Erdrick arriving after the first raid and presumedly dying when facing the Dragonlord. It ends with the ending of the first game and the prologue of the second game.
Why the hell would a bard need such an elaborate tomb? Sure, his silver harp summons monsters, but nobody in their right mind would want to use it. Dragon Lord? He's already commanding the monsters. The only thing that would make sense is that it'd sell like crazy. And that's only if the buyer was stupid enough not to know about the legend about a world-famous bard, which is quite unlikely.
Why do shopkeepers keep buying Cursed Belts from the hero (these can be farmed for cash early on, in fact). They pay good money for something that even says it's cursed. Who's buying these things?
Probably any priest capable of benediction would buy the cursed belt at a discount, remove the curse, and be left with a perfectly functional belt.
Also given that you can sell allegedly haunted items at a premium in real life, there could be a similar appeal in Alefgard.