>>20797681Sandstream and Snow Warning got nerfed.
No, really, that's literally the reason why. Being able to negate Weather damage with Leftovers was the only thing keeping Blissey ahead of Chansey in Gen V.
Note that in Gen V Ubers, where Groudon and Kyogre dominated every other weather inducer, Chansey was the superior blob because Sand was nonexistent and Hail was still Hail.