>>52304798Chansey isn't particularly magical or fae-like outside of it's mythical nutritious eggs, it's just rare and elusive. I think GameFreak also didn't want to just re-type every pink Gen 1 Normal-type to Fairy.
Though I do think Blissey should have been retyped as Normal/Fairy, as it has a much more fairy-like design with the white-wing ornaments, and would have made it stand-out more against Chansey. I love Chansey and Blissey, but Blissey's always felt a little unnecessary outside of the additional design flare it got.