Let's look at some allegedly "Safe For Work" submissions:
14 years ago
Buxom skunk in lingerie presenting her tits. http://www.furaffinity.net/view/6856582/
Male fox suddenly growing enormous breasts: http://www.furaffinity.net/view/1654295/
Gigantic and absurdly muscular wolf flexing while wearing a thong: http://www.furaffinity.net/view/4879630/
Nude guy grabbing his crotch. Title is "Half Cheetah. Half Roo. All sex": http://www.furaffinity.net/view/1151067/
Nude girl. Breasts (with nipples) in clear view. Ass takes up twice as much space in the picture as her head. Small bust size would probably make an unfamiliar viewer assume she's underage: http://www.furaffinity.net/view/6689339/
The same girl aiming her pussy at the camera while rubbing it: http://www.furaffinity.net/view/5742015/
Cartoon depiction of anal sex. Description includes the words "GAY SEX" and tags such as "butt" and "hump": http://www.furaffinity.net/view/5070510/
Page from a pornographic comic. Involves naked characters, talking about a drag show, and tags such as "poolsex", "blowjob", and "otter ass": http://www.furaffinity.net/view/5792188/
Depiction of a Digimon with watermelon-sized breasts. She is rubbing her breasts on a man's abs and is described as having sex with him immediately after. Comment section includes X-rated roleplaying: http://www.furaffinity.net/view/4454436/
Lesbian catgirls in small bikinis where the artist mentions how much her character loves incest: http://www.furaffinity.net/view/2576371/
An advertisement for incest pornography itself: http://www.furaffinity.net/view/5012047/
An advertisement for bondage pornography: http://www.furaffinity.net/view/2742655/
An advertisement for Sonic the Hedgehog pornography: http://www.furaffinity.net/view/2464098/
A 400 pound anthropomorphic dog in a speedo: http://www.furaffinity.net/view/6731765/
This took me all of 5 minutes to put together.
BUT THEY PUT NAKED ANIMALS IN CARTOONS SO IT'S OKAY RIGHT?
Male fox suddenly growing enormous breasts: http://www.furaffinity.net/view/1654295/
Gigantic and absurdly muscular wolf flexing while wearing a thong: http://www.furaffinity.net/view/4879630/
Nude guy grabbing his crotch. Title is "Half Cheetah. Half Roo. All sex": http://www.furaffinity.net/view/1151067/
Nude girl. Breasts (with nipples) in clear view. Ass takes up twice as much space in the picture as her head. Small bust size would probably make an unfamiliar viewer assume she's underage: http://www.furaffinity.net/view/6689339/
The same girl aiming her pussy at the camera while rubbing it: http://www.furaffinity.net/view/5742015/
Cartoon depiction of anal sex. Description includes the words "GAY SEX" and tags such as "butt" and "hump": http://www.furaffinity.net/view/5070510/
Page from a pornographic comic. Involves naked characters, talking about a drag show, and tags such as "poolsex", "blowjob", and "otter ass": http://www.furaffinity.net/view/5792188/
Depiction of a Digimon with watermelon-sized breasts. She is rubbing her breasts on a man's abs and is described as having sex with him immediately after. Comment section includes X-rated roleplaying: http://www.furaffinity.net/view/4454436/
Lesbian catgirls in small bikinis where the artist mentions how much her character loves incest: http://www.furaffinity.net/view/2576371/
An advertisement for incest pornography itself: http://www.furaffinity.net/view/5012047/
An advertisement for bondage pornography: http://www.furaffinity.net/view/2742655/
An advertisement for Sonic the Hedgehog pornography: http://www.furaffinity.net/view/2464098/
A 400 pound anthropomorphic dog in a speedo: http://www.furaffinity.net/view/6731765/
This took me all of 5 minutes to put together.
BUT THEY PUT NAKED ANIMALS IN CARTOONS SO IT'S OKAY RIGHT?
FA+

That's when appealing to the artists at any rate. I've given up hope trying to appeal to the admins for anything. Aside from just expecting inaction, I don't want to be repeatedly contacting them because then I would have their attention, and everyone I've seen hold the admins' attention for an extended period has ended up banned or harassed or excommunicated because they're so easy to offend.
Also people really shouldn't be checking FA at work period.
Either that, or they just don't think about it/care.
In fact speaking of people who are happy to draw loads of porn for money (but only because we're evil and force them to), check out this piece by Ajna, an excerpt from a "clean calendar that can be viewed by all ages": http://www.furaffinity.net/view/5126115/
It's a naked d-cupped rabbit wiggling her ass at the camera. I can't wait to hang that on the wall of my cubicle.
i think the dominant possibilities are that they either are losing perspective and don't really see it that way
and/or they don't really think there's any point in caring about categorization
after all, once you've had the safe-search turned off for a while, you forget that a porn-filtered FA is supposed to exist.
Most of the artists I've seen discussing it seem to genuinely think that these works are clean and would not seem strange to the general public, so I tend to lean toward the losing perspective theory.
and this was quite a few years ago
so the fact that i misunderstood not only the public acceptability of furry porn
but also the acceptability of really awful furry porn
goes to show how large those blinders can be
but sometimes pride drives an artist to seek any audience
even a disinterested or inappropriate one.
been there too