Comment by Galactic Navy Officer on Wolfie

@Wolfie My in-universe/Watsonian theory is the people doing deliberate Summoning are intentionally summoning younger people who are still inclined to listen to Authority without arguing too much. The intent to Summon those who will listen rather than question would also incline the Summoning toward cultures where authority is right and community is the priority are more important than individuality and the idea that Authority should be questioned.

The meta/Doylist reason is the original authors of modern isekai were seeking a POV character for a teenage audience, and not every author thinks through there are plenty of adults now reading isekai in all its forms.

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I specify modern isekai, since there are several 1990s and earlier stories I've seen that would qualify as isekai by present standards, but they were written long before what is usually thought of by the current use of "isekai." Things like some of the late 19th century to early 20th century fantastical stories, to the books Crystal Warriors and Crystal Sorcerers (though that was technically an accident), to the original He-Man: Masters of the Universe having the background that the current Queen was an Earth human who went through a space portal and landed on Eternia.