Why do you believe Girardi is worth 6 million a year? Serious question.
I think he's a capable #2/#3 defenseman for us now and can continue to perform in that role for at least another three or four years, at least. If the last year or two of his deal he begins to decline, $6M shouldn't hurt too bad barring some unforeseen collapse in the salary cap. I don't see Girardi's game falling off a cliff any time soon.
Also, there's something to be said for continuity. Too much roster turnover is problematic. We have a lot of guys potentially coming off the books, and I think it's important to keep key contributors if the cost is reasonable.
Girardi plays about 23 good minutes for us per night. We have to replace that if he walks or is traded. Do we have an in-house replacement? McIlrath may be ready next year, but not to assume Girardi's role. Stralman could leave. Klein is the only other right-handed defenseman. What will we find on the open market that is cheaper than Girardi but comparable to his skill? Will the cost savings of that player be worth the loss of continuity?