@Harmonie
I totally understand you there. It's a stupid cliche where it forces romance via suspension bridge effect.
However, personally, I do not see this as a way of forcing romance between the FL and ML, but rather for the siblings to see. To see that the man that their sister is marrying is one that can protect her. The siblings adore their big sister, the little sister especially, so it's a bit necessary to help ease the siblings into being more comfortable with the duke.