As the saying went, "Those close to pigs eat..." (cough), "those close to ink turn black..." (cough, at heart?).
People's values, interests, and so on were constantly influenced by their surroundings. Take Yukino Yukinoshita herself, for instance. At first, she had no interest in 2D culture, and her knowledge of anime had been limited to Mr. Pan the panda. Unfortunately, most of the people in the Service Club were seasoned 2D enthusiasts, to the point where she could now casually quote bits of 2D lore herself. Still...
Come to think of it, that was hardly surprising. Utaha Kasumigaoka could effortlessly turn all kinds of classic 2D references into weapons for her cutting remarks—or rather, for trading barbs with people. If Yukino could not even understand the insults being thrown at her, how much of a disadvantage would she be at?
Some might say that if you did not understand it anyway, being insulted did not matter; perhaps the other person would find it boring after talking for a while. But do not forget that most of the people in the Service Club were seasoned 2D enthusiasts. It did not matter if Yukino Yukinoshita could not understand—everyone else could!
Especially since that Doma bastard was always playing JoJo's Bizarre Adventure games with Masuzu Natsukawa, and everyone else understood them too...
Not to mention that the second daughter had accepted the request to help Mashiro become a famous manga artist. It was impossible for her not to pay attention to 2D culture. On top of that, 2D culture itself had a powerful pull. The more she learned about it, the more she felt it was not nearly as frightening as mainstream opinion made it out to be, so Yukino Yukinoshita had tacitly accepted it.
Even she had been influenced like that, so