for whatever reason, all pro catchers throw righty.

That REASON is that, on a steal of 3B, a right-handed catcher's shoulders and feet are already aligned properly to throw to 3B when he receives the pitch. A left-handed catcher's shoulders and feet must be realigned AFTER receiving the pitch resulting in a significant time loss, resulting often in a successful steal of 3B.

Video from Baseball Tonight where Keith Law discussed the promotion of Max Kepler.