By making the player make the first move, they empower the player to choose.
The problem often becomes that the entire sexuallity of mechanically bi characters or all characters in the game are often under player control. In a some circumstances games with this mechanism will have the characters who are not chosen as romantic options pair with no one ever or defer to straight behaviour. This is in deference to games wanting to have it's cake and eat it too.
Examples of this in action :
Stardew Valley where if you don't choose a same sex option to romance - no other characters ever have any romances ever. The one exception is Leah who has an ex who shows up late in the romance pursuit who tries to win her back. However, the ex is whatever gender the PC is so if it's a hetero relationship, it still appears to be a hetero relationship.
Harvest Moon Mineral Town (later editions) give the player to options to romance same sex options... But everyone you don't choose pairs up in hetero relationships and no other characters.
In both games there is no other queer rep so the player essentially opts in or out to all queer representation in the game. Blanket Heterosexuallity or bi-invisibility until given player approval is the default.
Indy games are generally the leaders for actual queer rep that isn't optional to the game's plot where characters sexuallities are not revealed by the player opt in.