Could a side issue be that the game format just wasn't sustainable? The sales steadily declined after Walking Dead because it's just more of the same?

FWIW, I thought the first Walking Dead was super interesting. It reminded me of those old Choose Your Adventure books. I had a blast playing it because it _felt_ like there was weight behind the decisions. After beating it, I started a fresh game so I could go through a totally different path / play style and... the illusion shattered. The choices didn't have any notable effect on the game.

And that was that. I just wasn't interested after the first game.