Re: Why in the world do people say that Choo doesn't hit well against lefty?
Well, technically this season he is not hitting well against lefties. He gets on base at a decent clip but he has a .526 OPS this season against left handed pitchers. That is very low. A slugging percentage of .206 is downright awful.
Career .681 OPS against lefties is pretty bad as well. Bruce has a career .757 OPS vs lefties and an .852 OPS this season, which is downright excellent.
I suppose the answer to your question of why do people say Choo doesn't hit lefties well is because he does not.