Why does Japanese anime almost always involve a summer festival? I've watched a lot of them, and almost all of them have this plotline

You're watching idol dramas about youthful emotions, for starters. Summer Matsuri is a traditional Japanese festival, anyway, it's a celebration to give thanks for something, wish for something, or something like that. Then, summer festival Japanese women to wear bathrobes, men can wear or not wear, itself contains the Japanese people on the tradition of so some inheritance and persistence, and which also vaguely exudes the tradition of rosy, and fireworks, dancing around the fire what a series of activities, so especially easy to happen something, a combination of all of the above, it is particularly suitable for the brewing and development of feelings. That's why Japanese anime has a lot of summer festivals.