Translation:Why is this book not released by them?
I think this needs to be "Why was," not "why is." Or: "Why has the book not been released by them?" (Because "released" must have already happened, whether active or passive, asking why such a thing "is," in the present, doesn't work.)
Does the word “released” have the meaning “published” here?
In this sentence, I think that's a very good alternative to the literal translation 'released'.
KBBI definition :
rilis/ri·lis/ v, merilis/me·ri·lis/ v 1 .......... 2 mengeluarkan (menerbitkan, mengadakan) buku, film, album lagu, dan sebagainya
Translated definition :
'to bring out', 'to publish', 'to make available', books, films, song albums, etc...