I have no doubt that that is why the book Forbidden (Tabitha Suzuma) ended as it did. She set out to make every aspect of that novel as sympathetic as possible. And she’s not the only author/creator who did that, I think you are entirely correct.
There’s an important distinction to be made – one that I confess I don’t usually bother making – between “tragedy because of society’s judgment” and a theme of “incest is destructive”. I usually lump it all into “not a happy ending”, but there’s one that’s sympathetic and one that is critical of incest. And the former, I think, sometimes falls under what you say. Often enough for it to be a trend.
EXACTLY. Sometimes people who are anti-incest try to use those unhappy endings to justify their own judgmental behavior. But really, many of those unhappy endings are actually showing what happens when innocent people are prosecuted just for being unconventional. You can usually tell when the author doesn’t care about the characters vs when the author is just trying to capture realism. The book ‘Forbidden’ seems like the 2nd kind, even though I haven’t read it yet… I can tell.