If two girls ever displayed yuri flags on stream, it's only because they treated female-on-female romance as such a joke that they're willing to always do it casually. In other words, it doesn't go beyond being fanservice for the viewers. This is because showing affection between females isn't as frowned upon as males showing affection between males. If a romance is a true romance, then they'd be more sensitive and shy about displaying them, no matter the gender.

This is why the "yuri" that you often see on stream isn't what you think it is.