Yeah, that seems to be the reason. People are reading this manga to see more of their chosen waifu, they want to see resolution for they waifu, and at best tolerate anything that is not directly about her. Yami? She's just an unimportant skank who dared to bare teeth at our waifu and steal her spotlight, in actuality our waifu and our waifu alone deserves to have the story be told about her, everything else is just an unimportant context for a side character with whom we don't need to attempt to empathize because she's not our waifu. If it is not about our waifu, it is not an effective narrative, at best it's a "sloppy text dump", nevermind that our waifu had 20 chapters of her own "sloppy text dump". Our third wheel of a waifu is not important in this arc where she has no reasons to be in the first place? That's, uh, bad pacing, and the story needs to be restructured in such a way where our waifu is always important, and it will all be about her, that would be good pacing! Now let's get back to our waifu, because I've been containing my climax for 6 months and cannot hold it anymore!
Pacing, momentum, climax - all buzzwords meant to be excuses for misreading this story. This complete dismissal of Yami and her story is nothing but waifuwars and reading the wrong manga. And I am saying this as someone whose waifu is Hikari, I couldn't care less about what happens to Yami after the story ends. Doesn't mean I wouldn't recognize the story that is being told, and the reasons it is being told the way it is.