Okay, so I gots me question. Roger's been dead for 20 years, so why exactly has no one claimed the One Piece treasure by now?
The 4 Emperors don't seem interested in One Piece, which is over in Raftel. Maybe no one knows how to get to Raftel. Maybe Raftel is an island similar to Sky Island where no one seriously knows how to get there, and it feels like a myth?
There's also the fact that most people have a tough time getting to the new world to begin with.
The marines probably wouldn't want to cruise in the new world partly because of the Emperors, for fear of starting war.
So you have a mish mash of people getting fucked before the red line, people getting fucked at shabondy due to it being so close to marineford and marine hq, you have people who probably are completely unable to compete with the Emperors and Warlords on an even level, we know so little about Raftel that there's probably a huge secret to get it probably related to ponleglyphs - so you'd have to able to at least decipher the old language.
It seems to me Shanks and Whitebeard aren't remotely interested in One Piece. Whitebeard already competed with Roger, and if he wanted it by now, he could have gotten it. He seems fine being the most powerful dude in the world. Shanks probably knows the secret to One Piece, but doesn't feel like there's much adventure in getting it since he already knows. Shanks passes on the dream to Luffy and Whitebeard to Ace.
At least that's what I think.
If someone were capable of getting One Piece by now, I'm sure they would have a long time ago. And that's half the mystery for me: why the fuck hasn't anyone gotten it?

ADVENTURE