As I said a very long time ago, we're clearly dealing with Lynn's exasperated dislike for any sort of interest that isn't taking care of an agoraphobic, out of touch sorehead who lives a life of self-willed helplessness. This means that instead of being the rather intriguing figure that I saw years ago on some sort of show about model railroading on PBS, John is presented as basically being a stupid overgrown child who takes something silly far too seriously. Why, he would rather worry about where some eyesore train set would go than the emotional needs of his own family.
This sort of thing is rather easy to understand when we remember that Lynn doesn't like to believe that people can actually be interested in things that confuse, irritate or bore her because she doesn't want to admit that she might actually be missing out on life. Just as she can't quite admit that lots of people enjoy Elvis because non-threatening non-emoters like Bobby Curtola aren't the apex of dreaminess and that people who like sports aren't yearning for the day they can visit ruin and slaughter on museums and libraries because she doesn't like to be uncomfortable, she can't get behind Rod's hobby because it takes him away from where she wants him to be.