I agree that well written dialogue can make or break romance on any day but usually these dialogues are set in the frame of a particular story that the game wants to tell.

E.g. In fire emblem you can only pair certain characters so you will only get dialogues for certain characters, but these characters have preset personalities and goals and attitudes and their dialogue reflects that

In this game the characters are suppose to be blank slates that you can form into whatever you want them to be. In his context I think it's hard to tell a romance story that can appeal to all users/play styles etc.