It's not that you're desensitized, it's that you're experienced. Experience makes you immune to trite attempts at tear-jerking
Also, Mother 3 is mostly held up as an example of great writing because of inertia. It's not. It's just become cool to say so. Kind of like how if you take any shitty Wings song Paul McCartney shit out and told people it was an unreleased Talking Heads song, they'd act like it's a masterpiece. Mother is a meme.