Because the St. Louis Cardinals could trade for Troy Tulowitzki, out of their enormous pile of prospects, we're never going to hear the end of rumors that they might, even though their apparent provenance suggests they're a little dated. As a blockbuster-trade-chit he's hard not to like: Going into his age-28 season he's got a career OPS+ of 117 and some extremely impressive defensive numbers. He wouldn't be blocking any can't-miss shortstop prospects in St. Louis, either, not that that's a question you generally ask about Troy Tulowitzki.
Meanwhile, his contract is—like the Matt Holliday deal on a larger scale—enormous but increasingly reasonable-looking, in the wake of other mega-contracts. From 2015 to 2019 he'll make $20 million a year before the deal ramps down to $14 million in 2020 and $15 million (against a $4 million buyout) in 2021.
Of course, last year's groin injury, which limited him to 47 games, and the wide swaths of time he missed in 2008 and 2010, leaves room for concern. But the real reason the Cardinals acquiring Troy Tulowitzki seems so far-fetched is that they've spent most of the John Mozeliak era seemingly building up to this moment—having a farm system filled with cheap, high-impact players who are all ready to go within the next year or two.
It's not that the Cardinals are afraid of dealing prospects; they've traded three recent first-rounders (Zack Cox, Brett Wallace, and Clay Mortensen) and one cost-controlled regular (Colby Rasmus) for veterans. But acquiring Tulowitzki—who is, for reference, a year-and-a-half younger than David Freese—would be a shift away from those distressed-asset deadline trades. It would reshape the team's payroll commitments for the rest of the decade, and it would require a prospect outlay like the Cardinals have never risked under Mozeliak.
Past moves don't guarantee future decisions, and it could just be that John Mozeliak has yet to find a franchise-shaking trade that suits him. But I won't put much stock in the Tulowitzki rumors until there's considerably more smoke.