According to a report from Yahoo! Sports, Ray Allen’s decision to leave the Celtics  and sign a three-year, $9.7 million deal with the Miami Heat  was based on not only the love shown by Heat president Pat Riley , but the lingering bitterness toward the Celts.
The report had a source saying “He felt he was getting respect that he hadn’t gotten from [Celtics president] Danny [Ainge] and [coach] Doc [Rivers ] anymore.’¦The presentation was incredible.”
According the author of the report, Adrian Wojnarowski, Allen still was upset that Celtics boss Danny Ainge had dangled him in trade talks, at one point telling the guard he was being shipped to Memphis only to then be told the deal was off. Allen was also reportedly upset over Doc Rivers taking away his starting job late in the season.
Then there was the fractured relationship Allen had with Celtics point guard Rajon Rondo . As Wojnarowski wrote:
Those were some of the conflicts that Allen had with Rondo, but the stubbornness of the point guard worked to exacerbate everything. Rondo and Allen were non-confrontational, but much of the behind-the-back sniping to teammates and those around the team took a toll. So much of it was sandbox stuff, the kind of grating, ultimately petty issues that occur in every locker room, every workplace. Rondo didn’t chase Allen out of Boston, but their relationship did become a drain in the locker room. Their cold war was something Allen discussed with associates, something that become a concern of management and the coaching staff.
“When it comes to basketball, Rondo is the smartest player on the team ‘ one of the smartest players in the league,” one locker-room source said. “And Ray considers himself a smart guy. But at some point, it became hard for Ray to be corrected by a guy so much younger than him.”
The report states that Kevin Garnett  and (to a lesser extent) Paul Pierce  both joined Rivers in trying to convince Allen to stay with the Celtics in the final days leading up to his agreement with the Heat. But the recruitment by Riley — who promised the end of any trade talks, along with the prospect of championship runs — won out.