Yasuke is actually a fantastic choice as far as history/narrative goes.
A shame the game looks like more generic Assassin's Creed Mapfucking+Crowd Supermurder.
Which is fine if that's your thing, but I haven't been thrilled by an AC game since... well, AC1.
Mirage was self contained, sold well, and was well liked by most. Shadows has a millioj controversies and the gameplay loop looks bad. Controcersy gets clicks so Mirage was ignored for more Shadows spam.
There’s also the whole “Ubi refused to allow it on Steam because they didn’t want Valve to eat their cake” side of things. Ubi believed that Mirage would have enough market pull for them to only release it on their internal Ubi store. It also has Denuvo, which many PC players despise. So nobody on PC bothered to play it, and it was only noteworthy for console players. Mirage only recently released on Steam, (I think around Halloween of last year?) but by that point any marketing that was done for it is old news and players have moved on. Ubi seems to have learned their lesson, because Shadows is releasing on Steam at the same time as the rest of the platforms.