This game has like a dozen LI's, and your complaint isn't relevant anyway, that's what having multiple saves are for. If the player chooses to only pursue one girl, and have one save, that is their own prerogative. It's not the developers job to provide content for every LI in every update, especially in a game that has as many as this game does.
As for the harem stuff, the only groupings that make sense have been posted about a ton (Katie+Friends, Monica/Zarah, Jen/Jolina, Wanda/Angel etc.). A large harem doesn't make sense, the girls personalities won't allow it without some major shift in who they are.
LOL, if I was only playing one game or this game was substantially different depending on which LI I selected then I would consider multiple saves. However, this game is not the only one I am playing, the game is almost exactly the same regardless of who the player chooses to fuck, the story isn't so compelling as to need several replays, and it is the developer's job to provide some reason for a player to come back to the game with each update. The game developer needs to entertain players with the content that is provided, if the player isn't entertained due to length between updates and then the lack of content once the update comes out the developer stands to lose players/subscribers.
If the mystery of the emailer was moving forward more quickly then the lack of content for the LI wouldn't be such a problem. The player could be excited by the fact that the "central mystery" is getting closer to a conclusion. However, that plotline has been a very slow burn and it doesn't even seem that solving it will impact the player's decision to either choose money or the girls (which is the central decision).
As to the "mini harems" idea Katie has stated that she won't share the MC at all and her friends seem inclined to be lesbians, Monica isn't inclined to share either, Zarah is pretty much a fuck buddy, Jen and Jolina seems seriously unlikely due to the privacy violation and distrust, Wanda and Angel haven't been seen in a long time and seem like side pieces with no importance to the story. That being said, as I am advocating for a non-canon "fan friendly" harem ending I don't see how any of that matters. The developer can still end the game with any player who cheated locked out of having a relationship with any of the girls, as it seems is the plan, and the mystery of the emailer solved.
