Personally, it's the animations themselves, but building on that it's the idea of adding animations - there is little to no way of animating things using AI that doesn't result in slop. When it comes to animated AI porn it's almost always the same similar and predictable set of movements that shrink dick. I attribute it to the fact that no open source models were trained on actual porn; you can use a lora but that only makes it less worse in my experience.
Animating would also make the scenes be less imaginary and more real, so instead of imagining yourself how the scene proceeds, it's explicitly shown as it should be, and if the way it's shown doesn't compare to the imaginary alternative then the animated scene has effectively been degraded in quality.
Your examples might have been simply unappealing to me in particular, but overall I think adding animations is risky.