I think it’s off the table primarily because if they ever actually wanted it to be on the table they’d have made an exception to it’s being de-canonized like they did for Darth Maul: Son of Dathomir.
Not sure I understand what you mean, I didn’t think Son of Dathomir was ever not canon.
They made an exception for it while it was being made, before de-canonizing everything. When the great de-canonizing occurred, that was the one title that was spared, due to it’s being adapted from a Clone Wars script. But it was still a Dark Horse comic, and everything else from Dark Horse’s run got turned into Legends. Son of Dathomir was basically singled out for sparing.
If they were willing to single that title out, they would have been willing to single out Zahn’s trilogy. But they weren’t. Probably because they’d already decided at the time there was not future in adapting it directly. And I think there isn’t for the reasons you laid out: Zahn wrote a Star Wars trilogy that is really more like a 6 or 9 film series in terms of how much story is packed in there, and the tone of it is definitely more like a crime procedural and a military fantasy than the space opera Star Wars is.
It was Zahn writing a great sci-fi military adventure using Star Wars characters. But I don’t know that it would work as an animated Star Wars story. It’s why they’re plucking out the star character and reinterpreting him instead of bringing the whole thing to bear.
I think it just wouldn’t fit with what the sequel trilogy is working with.