What really happened (sorry for the hyperbole):
Everyone within the Celtics were on board adding the necessary players to become contenders, while noone really wanted to ride Pierce's and KG's last seasons out, if we were only pretenders.
Danny probably tried a lot of stuff, even the token approaching of Dwight Howard, but every franchise he called asked for Rondo and the half kingdom, while not offering enough to make the Celtics true contenders.
Danny talked about this with Pierce, KG, and Doc (one at a time). They all agreed, that it didn't look like the Celtics were going to win it all, moreso with Rondo coming back from a major injury. And Danny said to each of them: "Well when I talked to the Clippers they asked if they could get Doc and KG in a package. Obviously I said no, but if we are going to blow it up, I might convince them to take Pierce, too. And the three of you can ride off into the Hollywood sunset..." (Who says no to that?)