We don't live in a cultural vacuum
Every era has competing cultural trends that 'look ahead' to where society is going (progressive), and that 'look backward' to an earlier, nostalgic time (retrospective). These cultural dynamics are not inherently 'good' or 'bad' – or even true, rather they broadly reflect the trends and social attitudes of their day.
Reading works from previous eras blur the sources. From our perspective today anything that is old is 'in the past', but put in the context of the time it was written it's easy to see which direction a particular work leans – hurtling towards a progressive future or retreating to a nostalgic past.
We lose nuance by dividing literature (all culture) into a polarized binary, but the reason works become critically important in their own lifetime is because the work speaks to the current zeitgeist. This polarizing dynamic between idealizing the past/condemning the past (to contrast everything today) is heavy-handed throughout history and art.
It's a fundamental schism of any era: are we headed in the right direction because the past was worse, or headed in the wrong direction because the past was better?
What is Faulkner doing right...?
Faulkner was the posterchild of the Southern Renaissance, a re-assertion of (white male) Southern voices after the defeat of the Civil War and collapse of Reconstruction. Southern Renaissance idealized antebellum life, seeing the past through a lens of nostalgia. Not coincidentally, the same era saw the revival of the KKK and the terrorism of lynchings on every front page. Conditions in the South were a hard dichotomy to the international modernism of art deco/skyscraper/flapper 1920s, yet both were simultaneously true.
The sub-genre offspring of Southern Renaissance is Southern Gothic, same setting and story elements but styled negatively where the metaphors hold up better today. Both 'unpack' the problems of the South but point towards different conclusions. It could also be said that Southern Renaissance was a cultural 'response' to the Harlem Renaissance, again culture does not happen in a vacuum.
Faulkner was the right voice in the right place and time to ride the Southern Renaissance trend. His style was a strong flavor of the Old South, and his stories are subtle enough to bring up a lot of problematic issues without being preachy about their meaning. He is, very firmly, a voice representing a nostalgic past. His 'purple prose' is part of the shtick. It was what the general public expected as the 'voice of the South'.
Contrast Faulkner with Mark Twain, a Southern writer (who lived in New York) from half a century earlier with a firmly modern and progressive voice – even writing science fiction. Twain was re-popularized during the Southern Renaissance too, so there is an on-going cultural dialog between progressive voices from the past, and nostalgic voices in the current day. They use the same language to say very different things.
Popular culture is a buffet of recycled tropes disconnected from their original context. That's how we know the Southern Renaisance movement had run its course, we got Margaret Mitchell's Gone With the Wind plundering Southern Renaissance as the backdrop for her 'strong female protagonist' romance. Mitchell cosplays and genre-bashes popular tropes and characters that don't historically fit together – Gone With the Wind is a female power fantasy romping around in a hoopskirt. She's not engaging in that social dialog of 'where have we been' and 'where are we going'. She's just having fun, and there's no clear message other than an outrageous MarySue as an anachronistic provocateur – she feels even more modern in an antebellum setting.
In hindsight, it all blurs together as 'Old South' pastiche. As writers, they are each saying very different things to very different people.
But as a culture we moved on. Mitchell got rich by jumping over a nostalgia shark on a motorcycle. Faulkner ended up in Hollywood doing re-writes on other people's scripts.
What am I doing wrong?
Publishing doesn't happen in a vacuum. Does your 'purple prose' also harken a return to earlier values? Is there some cultural reference or history that you are tapping by deliberately leveraging a particular style? Is this narrative voice a good match for your subjects and themes?
Or are you just 'too wordy'? No judgement. What you see as legitimate style, may hit readers as old fashioned. It might work for some themes and genres, but clash with others.
Faulkner wasn't just a guy with a lot of flowery words. His thick Southern identity was important in the context of the culture's re-examination of the South. His language evokes subtext and social constructions, cues which mirror his subjects and characters: slow, indirect, a veneer of propriety masking a loss in status – no different to how Raymond Chandler voiced pulp detectives in an abrupt 'street-wise' slang, and how Hemingway avoided all interior conflict and self-reflection in his stoic he-man characters. It's a narrative voice that matches the story.