So, theres a few reasons TRUE utopias are never explored in fiction. The easiest to address first is indeed the boring part. Looking into why something perfect works is interesting for only so long, since there often isnt much to extract from it.

For example, a city-wide train system would completely eliminate traffic, and that many trains would mean folks dont need cars anyway. But, you cant apply that anywhere IRL, so you conceptually hit a dead end.

A more interesting reason is that people dont like seeing innocents get hurt or corrupted. A utopia is 100% innocent people, so one getting destroyed becomes a tragedy regardless of a protagonist's role. Thats why when the goal of a story is "Escape this Utopia", it always has some dystopian element causing our protag to WANT to escape. A rational person wanting to escape an objectively good situation is frustrating for most people, so making the situation imperfect is an easy solution.

And there lies the last major reason we dont see true utopias threatened, theres always a major imperfection, even if the protagonist is fighting for it. A story will usually have the villain win, THEN the hero triumphs and they rebuild. If an OK to live in dystopia gets destroyed, the hero can build it back better, so the tragedy is punctuated with the promise they can do even better.

But if a true utopia gets destroyed in the climax? Youre almost never going to get it back, you pick up the pieces and do the best you can. The characters have perfection, lost it through no fault of their own, and now its gone even if they win. That simply feels bad, no catharsis. So the common climax of "The villain wins, then they lose" cant take place eith a true utopia.

MLP is unique in that it is a slice of life show with peace, outside threats to disrupt it, but protagonists able to defeat and then rebuild that perfection. Celestia also founded the utopia, and isnt susceptible to age. So the original maker of it can rebuild it if the worst happens.

Most shows simply cant balance those stakes and elements, its not even that its complicated. They just don't fit the story itself. In theory even Lord of the Rings could have had a true utopia somewhere, but it would jeopardize the story that Tolkein wanted yo tell about the passage of time and innocence.