Shanks took away the final piece of the puzzle, so he can make sure that nobody completes the puzzle without his approval.
Shanks had to make sure that nobody will obtain all four Road Poneglyphs, nor all three Ancient Weapons, and to do so, he knew he only had to take one Road Poneglyph instead of all four, because three of them without the 4th one are useless, so he knew he only had to take one instead of troubling himself with all four.
And to talk about the Ancient Weapon, remember back in Arabasta when Robin found the Poneglyph underground? That Poneglyph was protected by Arabasta kings for generations because it reveals the location of Pluton which is currently sleeping in Wano.
And another Poneglyph Robin found was in Skypiea, which was also protected by generations upon generations of the sky people because it revealed the location of the Ancient Weapon Poseidon.
Lastly, we only need one Poneglyph before going to the New World, the thing is, no Poneglyph appeared whatsoever other than the two Poneglyphs we already read, let alone a Poneglyph that is supposed to be protected for generations by a tribe. So, if Paradise (The first half of the Grand Line) didn’t have Uranus’ Poneglyph, it’s fine, maybe we will find its Poneglyph while we find the other Ancient Weapons right?
My guess of course not, not coincidentally anyways, I don’t think Uranus’ Poneglyph was simply not found or just delayed just because we simply didn’t run across it in Paradise. Uranus is too late for the game, we already found 2 Ancient Weapons physically up close and the Poneglyph for Uranus isn’t here yet?
It’s because Shanks took and hid it within wherever his territory is (possibly Elbaf) to make sure that nobody knows the location of the final Ancient Weapon Uranus because all those Poneglyphs that reveal the locations of the weapons could simply fall into the wrong hands and reveal the locations of the weapons to the wrong person. Shanks took one of the Poneglyphs because this way he can make sure that nobody lays hands on it, not under his watch.
To conclude, Shanks took away the final Road Poneglyph and the Poneglyph that reveals Uranus’ location which is probably hidden wherever Uranus is sleeping right now (Elbaf is a very high probability), this way he can guard the door to make sure that nobody can complete the puzzle without passing by him (Unless he approves otherwise.)
Theory by Reflxyy (https://www.reddit.com/user/Reflxyy)
