Shall I repeat that it's not the age of the smartphones and that information is something else on that world?
The Revos knew about it, the Yonkos knew about it, most truly important figures knew about it one way or another. Why didn't the albatross make it into a big deal? He probably knew as well, but there can be many reasons for him not to, like avoiding declaring war on WG.
Even with the Cobra incident, the only thing we have seen him write other than "Luffy is the 5th Yonko", what he wrote incriminating Sabo actually excuses the WG.
Remember that most people in the world of One Piece outside the Grand Line believe devil fruits to be a thing of legend, that's how bad communication is. Then there's the matter of trusting the information. People didn't immediatelly trust Vegapunk's words about climate change and even with the "proof" he gave of his honesty, a lot didn't. It would be even worse if the information were just random rumors or mouth to mouth.
Again, the frauds here that are creating a gaping hole in the narrative are the marines.