I don't mean that they want someone who Joe Fan recognizes, I mean they literally want to have a star-caliber player added. This is clearly an era where merely good teams are at a greater disadvantages, as the best teams load up as much as possible. The marginal benefit of Darvish over Cobb is greater for the Cubs(especially given their rotation situation) than it is for a team not smack dab in the middle of a competitive window. Darvish, Hendricks, Q, Lester/Chatwood makes for a much more potent playoff rotation than one without Darvish and with a different FA. I'll preface this with the thought that I've never been over the moon about Machado personally, even before he was a trade target. And I'm closer to a years of team control fetishist so I'm more inclined like you to see big moves be for people who stick around. But the front office is really smart and it's undeniable they have real interest in Machado at this point, so let's try to piece it together. If I had to guess, I'd say it's due to the SP market and the luxury tax. The Cubs could really use a pretty good SP to stay at the top of the NL pecking order, and not just someone you can squint and see a path to being real good, like Chatwood or Cobb. That means the FA options in this vein are Darvish or bust. Darvish isn't going to be cheap, and while it is possible to sign him and still get Harper next year, you probably have to get creative, and that's before the reality of the 2018 season happens. Maybe a key pitcher like Quintana or Morrow has their shoulder blow up in August. Now your margin for error gets all the more thin and maybe involves some sub-ideal options like bribing a team to take on a contract(Zobrist? Lester?) with actual good players. So if the FA option is a narrow path, then we're left with the trade market. The Cubs could trade Happ or Almora without a ton of hurt, but the prospect pool is thin enough behind them and those 2 have enough flaws that it limits the market of pitcher you can get, you're probably back to doing more hoping that the pitcher is real good than you want. But, what if there was a way to open yourself up to get a higher end trade candidate? That would involve Russell, who has the best combo of team control, youth, and potential of the non-Rizzo/Bryant/Contreras position players. Sure you could do that straight up and move Baez to SS, but that itself is a downgrade that mitigates the benefit. Insert Machado. You use other players to get Machado where the downgrade is much more marginal(Montgomery and Almora can be replaced without a lot of tears, for example). Now you can use Russell to get your SP that belongs in a playoff rotation, and you've also gotten a sizable upgrade for this year(a peak competitive year) on top of that. This fits much more cleanly into the luxury tax because Machado's money disappears after 2018, and the SP you acquire is going to make far less than Cobb/Darvish. Said another way, I'll go back to my point at the top, this is about stars. Trading for Machado and using Russell for a good SP maximizes your stars in 2018, and it's the path that makes it easiest to get another star player(almost certainly Harper) to replace Machado in the long run. You can possibly do that another way, but it could get dicey and has its own downsides.