Bigger EDC for Winter Carry.

I must be missing something. They are literally the same size. Why not just carry the .38 year-round?

While they are the same size they're NOT the same weight or capacity. The 22 Mag is 12oz and 7 shots with very low recoil while the 38 Spl is only a 5 shot and 16oz and has a lot more recoil. Just because they look the same doesn't mean that they are the same by a long shot.