Maybe I missed something, but I feel like pretty much everyone is overlooking the fact that fantasy is...not real???? ^^;;;
Like, I can see why people tend to carry around the ingrained notion that nobles and royalty are inherently more important and have lives that are more worth writing about, it's probably been carved into our brains for millennia at this point.
But we're not talking about historical fiction, we're talking about fantasy fiction. Stories where miracles and magic are real...stories where maybe being born into the ruling class doesn't have to be the only way to escape a life of drudgery and poverty.
Stories that don't even have to be set in societies based on the feudal system! Fantasy =/= Medieval Europe!
With that in mind, I'd chalk it up to a lack of imagination, simple as that. :T In real life, the elites have all the power, so even in worlds with fictional powers that could potentially go to anyone, authors continue to hand them over to the elites, and even to posit that they belong there.
Half of 'underdog' fantasy stories have the MC discover that they're the secret long-lost prince/princess of a powerful kingdom, because of course that's the only sensible reason for them to be special and talented...and another large portion have the underdog earn royal authority through power. Like, even if they really do start out as just a nobody from nowhere, the natural endgame for them should be to become a king or queen. Because that's apparently what power is for...
Personally I have two major fantasy stories in the works where the main characters are nobles, but their status isn't idolized by any means. In one of them, the unending attention that comes with being the 'Little Princess' only contributes to the MC's anxiety issues, and although she's relatively young she already feels that people see her only for what she is, and not for who she is. She shares the spotlight with three other nobles who have been literally banished from their families, their lands, or the universe as a whole for some degree of nonconformity, and their aim isn't to restore what they've lost, but to tear the whole system apart and start over.
In the other one (which is much more difficult to write...) the MC develops similar anxieties about her position of power through seeing it actively used as a weapon to destroy and subjugate others. She's supposed to be the legacy of martyrs and the poster child of the 'master race', but at heart she doesn't want to hurt anyone and is desperate for a way out. And although I haven't worked that much with her, I think her character arc will probably revolve around developing a backbone, taking back her authority for herself, and using it to redefine her role in society as she grows to understand it.
...Basically, even if you insist on writing about nobles, and even if it's more realistic in the world of your story, that still doesn't necessitate glorifying the position, or otherwise crafting a story where only the opinions/experiences of the ruling class are worth consideration.