Plugging back into Dean’s thirst for normalcy, I wonder if maybe he found it comforting to have his father die of something that tons of other people die of all the time instead of at the hands of a demon.
I was initially disappointed that John Winchester wasn’t going to appear in the episode, but now I think it might have been for the best. Having him around would have meant not giving Mary the focus she deserved. And his absence provided for Dean’s terrific soliloquy in front of John’s gravestone.