Is it really that surprising that writers would want it to be true?

It is unsurprising only if you fail to consider the implications of it being true (in the strong sense).

Some languages have extremely complex ways of indicating tense (making a grammatical distinction between, for example, past events that occurred and then ceased, versus past events that are still ongoing). Some have retained complex grammars for expressing wishes (the optative mood, for example). Other languages have far fewer grammatical ways of expressing tense and mood. Tenses in Mandarin Chinese are often "optional" in a sentence, for example, and in general the mood system of English is a lot simpler than it is in, say, ancient Greek. Ancient Hebrew, strictly speaking, does not have past, present, and future tenses at all (but instead combines context with perfective and imperfective aspects).

Now here's the possibly dangerous leap. "The Chinese think differently about time" (or are less concerned about it). "The ancient Hebrews were very focused on the present and rather feckless about the future." "German and Greek are the only languages worthy of philosophy" (a direct quote from Heidegger). "There are certain emotions in Hopi that cannot be expressed in English." "People speaking a creole are less capable of nuanced rational thought." You can probably see where this is going . . .

One of the more interesting grammatical features is evidentiallity, which requires you to indicate how you know what you say, e.g. if you saw it, deduced it, or if it's something you were told.

Another is grammatical honorifics, which use suffixes to indicate your relationship with the speaker and sometimes also with who, or even what you are talking about.

Same reason writers insist that reading literary fiction gives you a true and deep understanding of the human condition unachievable by any other means.

A huge problem in fiction is that it usually greatly overestimates people's ability to understand each other. Characters never make mistakes reading each other (unless it's a part of the plot) When they see something one on another, it's assumed to be true, even though in reality this is extremely unreliable.

Habitual readers of fiction tend to be a chore to deal with, as they overestimate their ability to read and understand the thinking of others, inadequatelly communicate as they assume you should be able to read them, and blame any of the inevitable errors on intentional deception from your side.

A strong formulation of the idea/theory is unsupported. But, a weaker version is hard to deny, at least entirely.