>>725813831
Because the Yasuke presented in Shadows would have been known for all the things he did by basically everyone to this day including people in the west just for how much he singlehandedly shaped Japan's trajectory as a whole. That's the first issue.
The second issue is that a black man who even in-game is 1 foot taller tan anyone else and is regularly referred to as an oni/giant wandering around murdering Japanese people would be something everyone documents.
The third issue is that there would be no way any civilian would be selling this black man weaponry. Short of him murdering them for their weaponry they would instantly be blamed for anything he does with that weaponry or at the very least have things traced back to them, and he would constantly be accosted for wearing weaponry at all.
Yasuke in Shadows is complete nonsense in terms of believability. I don't want to type this all out again so refer to here >>725805961, but it is impossible to believe the Yasuke presented in Shadows would have so little written about him when people who did significantly less important things than him like teach a sword style have their entire life known about them.