I feel like Danbooru sometimes deletes things for very strange reasons. I see nothing wrong with this pic.

Basically the "did not like the post enough to approve it" it's a way to soft "approvers didn't care enough about this image". I've encountered so many images with a decent, even good quality, but that gets deleted.

*Shrugs* What can you do I guess.

As an uploader, I would've passed over this if I saw it on Pixiv because the shading and lineart aren't very good (and something bothers me about the hands). It's hard to put into words (usually I would just skip something without needing to know why I didn't like it), but it has several telltale signs of "art that won't get approved on Danbooru," and after staring at it for like an hour I think I can explain why.

It's easier if I compare it to a much better work by the same artist, post #2921573. In that post, the lines and shading work together to effectively depict the folds of the clothes. The shading is entirely areas of unblended colors, but the light and dark areas (as well as the choice of how light/dark to make them) are placed in a way to give a sense of depth.

Here, the lines are sharp and thin and angular, which make figures feel flat. Instead of unblended areas of color, the artist has used gradients, but that has backfired because it prevents the viewer's mind from being able to fill in the textures of the cloth. Everything looks plasticly smooth. and the dark areas seem haphazardly placed (for example, compare the way the brown-haired girl's hair is shaded here to the way the gray-haired girl's hair is shaded on the other post), so instead of creating depth, they're just. there. It feels like the artist is working on using more complicated shading styles than the unblended color areas of the other post, but they haven't developed it enough yet.