He's not going to sign an extension because he'll make a lot more money if he hits free agency -- I wouldn't read more into it than that.
You are so sure of that. I still think Rondo might see an advantage in securing his future and his home for the next four years this summer and not having to deal with the stress, the scrutiny, and the risk of being derailed by re-injury which would come with waiting it out until free agency the following summer.
I realize it's a substantial difference in potential dollar amount, but, still I wouldn't be surprised if he took that security. On the other hand, I won't be surprised if he waits until free agency either.