The only reason I can think of (and note, I do not agree with this, simply trying to think like teh Cubs) would be fear that a late season slump would kill trade value. As is, they can talk up his 10 homers in 170 some odd at bats and try to sell it as "imagine that over a full season". If he tanked, the homers may not have a sexy SLG percentage to go with them. Absolutely stupid, but it makes more sense than the likely reason. That he isn't a slick defender. But hey, toss him out at second this winter and see what happens. :-))