I'm puzzled by Train Dreams

Finished Denis Johnson's novella "Train Dreams" and have to say I'm puzzled - the novella truly has some great scenes, most notably the protagonist, Robert Grainier, slowly making his way into the forest after the earth-scorching fire that consumed his cabin and killed his wife and daughter, and Grainier, at a later stage in his life, running a hauling service and transporting a wounded man (shot by his own dog) through a lonely forest at night, the two laconic men engaging in some dialogue, at first very funny and gradually becoming edgier and more creepy, as the wounded man talks about ghostly characters that haunt the woods. Some other very fine descriptive passages as well: the young man hauling sacks onto a wagon who says he's feeling dizzy and then falls to the ground dead is another example. Fine writing throughout - and yet, and yet - really what does it all add up to? As readers of these posts will know, I do look for plot and an arc of a story in the fiction I read - and in a way that's especially true of a novella, a form perfectly designed for a single fictive action that has a beginning, middle, and end - or, put another way, crisis, conflict, resolution. Train Dreams does not - the plot jumps around a bit in time, and that's OK if all the pieces are place by the end - but in TD the elements of a plot never gel: at one point I thought the story would be about Grainier's attempt to find his daughter, who may have survived the fire. It's not that the plot has to encompass a single action, though that's good when and is a staple of the greatest of novellas - see James, Chekhov, "The Dead," "The Bear," A Month in the Country, Light on the Piazza - and so on - but another possibility is to watch a character change, evolve over a long period of time, and I don't believe that really happens satisfactorily in TD: Grainier is a sad and lonely youth, blessed with a happy late marriage, which we see for a moment only, and then suffering a loss, and for the rest of his life he's a social isolate, as best we can tell. He doesn't change radically - and the world around him doesn't change radically, either. Part of the theme is man v nature, but that's not developed in any thorough way. I don't know - I will definitely re-read, but as of now I see a lot of great elements here but I don't get the overall picture.