Maybe he legitimately didn't want to go to the Mariners, but as for the rest of them, this seems more likely:
These lists can usually be changed each off-season, and they generally are adjusted for leverage purposes. Agents stay on top of the rumor mill, and they figure out where the most likely destinations are for their client if he is going to be traded, then choose those organizations as the teams to block, giving them the most amount of leverage possible.