There are three ways to interpret the Eddie Guardado experience. First, and by far the most likely, Mike Rizzo gave him an invite to camp thinking he was worth a look, he wasn't impressed, and now Everyday Eddie's gone. Simple as that.
The second theory is that Rizzo really did think what Bill Ladson and Tom Boswell 'reported,' that Guardado was considered an important signing for the team, and by cutting him so quickly, he's showing some fairly erratic judgment. Frankly I just don't buy that at all. Ladson and Boswell write dumb stuff all the time, and John Dever sometimes tries to hard to make news where there isn't any. Rizzo doesn't have a track record of massively overvaluing obviously bad pitchers. It just doesn't pass the ol' Occam's razor test.
The third possibility is the rosiest. Rizzo signed Guardado in order to have a fall-back plan on hand in case something goes wrong with the first 7-8 relief pitchers he actually expected to use. This is good practice and is to be applauded. You don't want to get to opening day with no options in case, oh let's say your plan for Mike Hinckley to indefinitely maintain a zero ERA falls through.
But perhaps Rizzo's willingness to move on quickly from Guardado is a sign that he's feeling better than he expected to at this point about plan A. Perhaps he's feeling confident about the so-so veterans like Sean Burnett, Brian Bruney, Tyler Clippard, and Jason Bergmann to give him 60 solidly so-so innings each--or that maybe one of those guys might be even better than that. Maybe he's looking at Drew Storen and thinking he really does have this year's Andrew Bailey on his hands. Maybe he's looking at young guys like Luis Atilano and Atahualpa Severino, and thinking, "ok, that'll play." Maybe he's just (knock on wood) seeing fewer injuries than you have to plan for.
(Now, before you go posting double-digit spring training ERAs in the comments, let me repeat that I think this is pretty unlikely, and I'm choosing for one day to throw out some happy thoughts, so lemme have my moment ok?)
There's actually a fourth theory that pops to mind, which is that Stan Kasten, in his insatiable need to show players and agents what a big strong man he is, decided to mess with Guardado to get back at him for the bad press he got after the "the effing Nationals?!?" incident in 2008. That's probably not what happened, but I bet Stan wishes it had.