Why is Sachiko so unpopular? I think it's a combination of multiple reasons.
Her voicebank is specifically designed for one rather niche genre (enka). It's listed that she's suitable for Jazz and Blues too, which like, yeah, because they tend to have a slow tempo and sound dissonant on purpose, but when I think of Jazz and Blues I think of American music, and Sachiko doesn't have any English capabilities. She is actually so heavily accented that Engrish is beyond impossible with her.
She tends to have a very slow consonant velocity. When I try making her sing a regular song, I crank the consonant velocity to the max, but most of the time it makes no difference anyway. But I do love her unique accent and sensitivity to pitchbends. Her especially accented consonants like "k" inspired my UTAU's -banshee- voicebank. But he's not as awesome as Sachiko.......
So her voicebank is rather difficult to use, but so might be OLIVER, and Oliver is pretty famous internationally. Which is why I think all other things about her also contribute.
First of all I think the name "Sachiko", just "Sachiko", no kana or last name, is boring branding. "Sachiko" is just a rather common first name so search engine optimization hurts her.
Also her character design is spectacular. It's very spectacular. I think the main focus of her silhouette are her huge kimono sleeves with the speaker cylinders on them, but besides that she just looks like a flurry of patterns and colors. Which is an amazing illustration, but it also makes her difficult to draw! Fanart is incredibly important for a Vocaloid's brand and reputation! Most artists will be forced to simplify her design or put her in an entirely new outfit to draw her, and she won't look like herself anymore. People already compare her to Meiko a lot because they both have short brown hair (although Sachiko has a mullet and Meiko has a bob..)... And they both wear red...
Another terrible thing you'll find if you try to draw her; you'll find that she has no official art besides this one standing picture... And the standing picture is 800px in height, compressed, so you can't see half of the details on her outfit.
This actually led me down a rabbit hole. I realized that at no point in history has Yamaha ever published a PNG of Sachiko that is larger than 900px, but I realized that a larger version of her standing picture MUST exist because back in 2015 when producers were commissioned to make original songs with her to promote her, some of them used HD versions of her illustration for the music videos. But all of those images are zoomed in on her face and torso. I scoured the Wayback Machine for all possible official articles about Sachiko and I didn't find any larger images. If anything, the fullbody illustration that's up on her Vocaloid.net page right now is the smallest its ever been.
So I went ahead and messaged her illustrator, Foo Midori, on Twitter, to ask them if they have a HD version of the illustration and if they can share it with the fans. But they just told me that the full illustration should be on the Vocaloid website and then when I clarified it's a small image, they never responded again...lol
I don't suppose that her CD comes with a PNG of the full size illustration... So it might be lost media forever.
