You know, except when people either personally ask for that advice specifically. Enter a creative writing contest, or anything that invokes competition and begs to be critiqued for such a thing specifically. Or, perhaps how literally every single writing/literary agent works, when it comes to endless revisions required to getting one's writing published. Then, it benefits the writer significantly. But sure, all other times, no reason to rewrite things whatsoever. ^-^'
(Or when you're writing a fan fiction, because hey guess what, that's rewriting/changing someone's established 'voice/cannon' and making it your own. And that's okay too.)
Professional editors generally don't edit someone's prose to fit their own wants. Professional editors generally focus on grammatical or stylistic errors that are unambiguously bad form, spelling errors, misuse of semicolons, that sort of thing. When they're not, they ask the author questions about their choices rather than simply correcting them without author input, and those corrections generally aren't based on the editor's preference or making something "better", they're based on making the text more appealing to a target audience, removing slang that a target audience might not understand and such.
Fanfiction isn't rewriting someone's established voice? That's like saying every time someone uses Dracula they're rewriting Bram Stoker, or every time someone uses Sherlock Holmes they're rewriting Arthur Conan Doyle. Fanfiction is using someone else's creations to tell your own story, it's not at all "rewriting someone else's voice", that's absurd.
This sentiment could easily boil down to "the author can never be wrong/all writing quality is subjective."
I'm going to let you in on something, when it comes to storytelling? There is no objective quality. Sure, grammar and punctuation have objective quality, but the story itself has no objective quality. Your opinion on a story is never the objective truth no matter how highly you may think of yourself. An objective truth is "This text is white", if you brought an uncontacted tribe to my screen and taught them English, they would say this text is white, it's objective, nobody can argue that this text isn't white, quality of writing is not objective no matter how popular an opinion is. It's not a sentiment to say that all writing quality is subjective, it's objective truth.
But all suggestions can either be taken with sheer hostility and ignored. Or they can be evaluated and worked upon. (And I can tell you the latter makes you more successful in every avenue and medium.)
If quality was objective this would be true, but quality is subjective, so suggestions are based entirely off of opinion, and the author doesn't have any more obligation to listen to your opinion than the president does, in the end it's not your call, and many pieces of fiction are better because the creator didn't listen to criticism that didn't match their vision, and many pieces of fiction are worse because they did. Tvtropes has an entire page of this called "It will never catch on" of criticism that was roundly ignored and proven entirely incorrect once the work came out.
And, tell me this...
How can you critique anyone's writing choices whatsoever, when you aren't allow to seek or offer a change?
You're allowed to, but nobody is under any obligation to listen to you, and if you present those criticisms in an impolite way, say completely rewriting their work in your own style without their permission and saying yours is the superior piece, then they're far, far less likely to care what you have to say.