Is this picture inappropriate?

If you try to post this picture in the daily challenge, it will be called inappropriate.
By the way, it doesn't have the eye mark (regulation mark).

Is it because of the invisible pants?
Or is it because of the shinai (weapon) I carry on my back, even though I am a kendo beginner?
I am not convinced what is the cause of the problem, even though the Seaart homepage allows (and even permits) the posting of genitals that are transparent and visible, not to mention the chikubi and underwear.
Please give us a satisfactory explanation, instead of just responding with a canned response that has no meaning or cause, "Because the content of the postings contains pornography, violence, or violates community guidelines that are considered inappropriate in a public forum.