Ohtani has yet to play in cold weather or east of the Mississippi.

Shohei Ohtani has been DH in five road games with these high/low temperatures those days:

March 29 84/49 Oakland, CA

April 10 71/47 Arlington, TX

April 11 79/50​ Arlington, TX

April 12 84/54 Kansas City, MO

April 13 83/54 Kansas City, MO

His two road game as a pitcher:

April 1 74/48 Oakland, CA

April 24 indoors in Houston, TX

His home games are in Anaheim, CA.

Maybe that's why he wanted to play on a west coast team: good weather.