It's weird that this thread is acting like this hasn't been a common feature of HBO For twenty years.

Six Feet Under, Deadwood, and Rome, those "early days, pioneers" of serialized TV all heavily featured incest based subplots.

Rome was the most incredibly baffling one because it was the least narratively condemning of it and it was never even marginally alluded to at any point in history between those two characters. They built up the character of Octavia and then had her fuck her brother, while also floating familial sexual tension throughout both seasons and even explicitly calling on a young Octavian to have sex with his uncle.

Incest is everywhere in the Rome show.

One of Six Feet Under's biggest plots is Billy's unrequited sexual attraction to his sister, which she rejects outright, but quietly entertains and is frequently curious about in private.

Deadwood's Joanie Stubbs was a character all about incest and how that affected her life and her future relationships.

Boardwalk Empire featured paternal incest.

Bored to Death had incest. Arguably manipulative incest.

It's hard to find a time when HBO isn't running incest and at times aren't jamming incest in for some reason where it doesn't belong. Then, of course, its two flagship shows are about Incest: The Movie - The Musical (The Series) in ASOIAF.

You can argue this or that about its motive, but you can't argue its frequency nor the fact that HBO seems to ask if there's a way to shovel some incest into your script.