Well, first off, at least for the Japanese, those guys either have to reach free agency over there or get their teams to cooperate (which they rarely do). Another concern with the Japanese is their usage patterns--they're used far harder than American pitchers, and it tends to show up as they age. Combine that with the teams' reluctance to give up until the bitter end, the Japanese pitchers that get over here often don't and won't have a lot of good years left. Don't get me wrong--I love their talent, but just not the chances of seeing a lot of it at or near their best in the major leagues.
Seen on a bumper sticker: If only closed minds came with closed mouths.
Some minds are like concrete--thoroughly mixed up and permanently set.