To put it a bit less bluntly: because this is the dev's story.So I posted here once or twice and have seen people like me having Kayane as a favorite, so how so she still have no content?
In theory: the dev has a story he's telling, with some overlap in plot threads. It's possible that there will be events with Kayane, but that there's a story reason to delay them (for example, she's a confidential informant for the police, who can ultimately provide assistance with the hornyness drug plot line at the least, but needs to maintain her cover for now, leaving the MC having to deal with that on his own for now).
(Yes, I realize that that plot line, as well as the one focused on his revenge, are somewhat stalled at the moment: hence, the "in theory.")
I do tend to agree that those two main plots seemed headed for resolution a couple of years ago. I will note that he apparently no longer talks about what was supposed to be his next project (Waifu Hunter, I believe), and suspect some aspect of his plans for that fell through, leaving him needing to stretch this project out somewhat. Ending it without some sort of follow-up probably would lose him most of his Patreon support.