Two things:
1. To those who are clamoring for Doc to uphold his end of the "bargain":
I really don't want Doc to coach a rebuilding team, if that is the direction that we are going.
2. Perhaps Doc is keeping his mouth shut out of loyalty to the organization:
If Doc announces he is leaving, everybody (read other GMs specifically)would believe that the Cs have made the decision that Pierce won't be back. If they believe that decision has been made, that weakens Danny's bargaining position of getting value for Pierce, since the other GMs know that this is a done deal, as opposed to Danny being able to say in negotiations that HE still isn't sure of the direction of the organization and therefore needs to be somewhat impressed by an offer to trade Pierce ('s contract).