Having some of the women later allows for more opportunity to develop them further. For instance, I know next to nothing about Amity's motivations; having Witter hold more in-depth conversations with her could logically progress them toward something romantic later. In the case of Roxanne, she's been more like a boss than a motherly figure, so while they would definitely be closer than Witter and Amity, they haven't had much in the way of moving in a romantic direction yet. I'd expect you'd need some time to develop that storyline.
While Ketha has been resisting temptation (unless you're on NTR), I do feel like her loneliness will eventually give way and something could flower between her and the MC. If you kissed Myra, Ai had her heart broken a bit. If you didn't, Myra is a bit disappointed and also felt a bit of heartbreak. In both cases, though, because they do have romantic feelings for Witter, I feel like saying and doing the right things to each
could mend their relationships. As for getting them to accept an eventual harem, well, I'll let your creativity decide that.
