we moved here for a change of heart
We can only guess what Andy's pre-existing faults are. Played by Chevy Chase, we can assume he's a casually sarcastic asshole, but just funny enough that people who are around him often enough find him amusing. We can only guess what Elizabeth saw in him however long ago they got together. Hell, we don't know what she does (or has done) day to day [actually, later in the film, we learn she was a schoolteacher, but other than Andy saying as much, there is no reason for this to be fact], or what she wants out of life. She is very much a prop in Andy's story, and their relationship is only as genuine as any given scene needs it to be.
Not that the movie doesn't let them have some interesting interactions, but to what end? She lies about the apple, he steals her manuscript, and these two things are, as far as the film is concerned, equally wrong, both of them worthy of divorce, both of them worthy of forgiveness.
So, nevermind the plot, nevermind the relationship. Think instead of the expectation Andy has from the country life.Think of what Elizabeth expects. He expects to be able to sit down in his writing room and crank out a great novel. She expects a comfortable life away from the trappings of the city. And, they both expect to start a family. It's a conservative dream--move to the country, raise up some kids in isolated bliss where the larger problems of the world don't mean a thing.
First day in the new house--after the movers arrive, anyway--Andy sits in his wet office chair and writes little more than a title and his own name, then ally's asleep. Elizabeth starts digging in the garden and finds a dead body, because the film has no room for them to have actual problems that tells us about their personalities, their urges, their goals. Andy wants to write. He can't. Move on to silly antics like bumping into a doorknob, dropping Elizabeth, their phone registering as a pay phone, getting into a fishing competition that goes badly, eating testicles, buying a dog that has no interest in being a pet, etcetera. This movie is basically, rural location is going to do what it wants, the people there will fuck with you, nature will attack you, and you are mad to even bother being there. And, at no point to Andy or Elizabeth get better at it. They just decide to stay. They don't even get better at their relationship. They just announce they want to still be together and everything is fine. Redbud is still Redbud, the Farmers haven't earned any change, but change happens because the movie has to end and we have to pretend that any of it mattered beyond a few laughs.
Scene to scene, nothing much matters. Andy catches a snake while fishing, it gets inside the house, Elizabeth screams, CUT TO in the car Andy says he's been too busy writing--he hasn't been--to notice she's cooped up--she isn't. The movie has an essential disconnect between its action and its dialogue, and rather deliberately so. In any given moment, only what we are told matters. Never anything deeper.
There is room for more. I mean, offscreen, Elizabeth becomes friends with Mrs. Dinges. Offscreen, Andy spends too much time drinking with the Criterion brothers. These are more interesting, more character-driven things, but we don't see them. Instead we see Elizabeth break down in tears after what seems like two days in the new house. And, then she--offscreen--writes a children's book and I think it's fine if Andy has a problem with that because we should have a problem with that. Online, people have problems with supposed "plot holes" in movies all the time. This movie has a giant plot hole right at its center. Without the movie even seeming to know about it, one of its two leads has created her own subplot that she forgot to want in the first place. (We see glimpses of her writing on legal pads, but barely.) Meanwhile, the other lead fails at his dream... because... I guess failure is funny, even when these is no reason for it.
Writer's block as a storyline would be fine if the film has established better that Andy could ever write in the first place, or if his writing problems somehow stemmed specifically from being in the country. And, his bad writing would matter if we heard some of it. Instead, we have to trust Elizabeth's opinion, when we have no reason to think she would have any idea about it in the first place. And we just have to believe her, and we have to quash Andy's dreams, too.