Something I noticed while watching a lot of popular anime based on Light Novels that focuses on slice of life for the most (Oregairu, Haruhi Suzumiya, Oreimo, etc.) is that they never stated where in Japan is the story actually taking place. In a lot of cases I noted that these settings tend to be a non-decrepit small to medium sized town with a school, and yet at other times, despite this ambiguity, the characters visit an identifiable real life locale, such as Oreimo with the Akihabara district, which seems to imply that the series happen around Tokyo. I can understand if the anime adaptation would not bother mentioning the setting, but is this ever touched upon in the original Light Novel source or has it always been sort of a case of the "Springfield" trope in play? Is it possible that there is some kind of general assumption by the Japanese populace that all series happen in Tokyo or something?
The Haruhi Suzumiya series is mainly set in Nishinomiya, Japan.
The Oreimo series is mainly set in Chiba, Japan.
It's quite obvious by the mentions in the Oregairu series novel and various episodes that the main setting of the series is based in Chiba, Japan as well.
Each author has their own reason for explicitly stating, excluding, or obscuring the main setting (just like the writers of the The Simpsons). There is no set rule in literature about whether or not the main setting needs to be explicitly stated, especially if it's fiction. A lot of fiction writers like to base their story on familiar settings, so that it's more easily related to readers (the Japanese audience being the primary readers) or give the author a easier time when they are world building. There is no trope in play, how much an author is willing to reveals about the setting of their story is up to them. Sometimes it's not the modern-day Japan as most would know it as, but such embellishment are implied and accepted by most readers of fiction.