Because Joyboy seems to be a legendary figure that was literally erased from history lol.
I understand where youre coming from but its pretty cut and dry imo.
VP literally only mentioned JB nobody else, if there were others near his level why are they not mentioned in the Poneglyphs?
Rocks, he was deleted from history... only difference is he didn't leave behind poneglyphs and it's only been 40 or so years since he's been deleted.
We don't know anybody else from that era, because there's no record of anybody else from that era. If the Monkey D. family is producing arguably the strongest figures of each generation, I don't see why they would be different in the past when the Ds were at their peak? The lineage holds insane potential.
Marshal D.
Trafalgar D.
Monkey D.
Gol D.
Portagas D.
Rocks D.
These families are producing top tiers in a "watered" down era. You don't think they produced people who could challenge Joyboy when the D clan was at their peak?
We literally only know about the contents of like 2-3 historical poneglyphs. And Joyboy is mentioned in only one of them iirc, the message to Poseidon, which he wrote himself. None of the others mention Joyboy (Maybe the Ohara one?? idk).