Miami was able to offer him something more, something better.
South Beach didn't sell him on the weather or the fans (obviously). The Heat sold him on LeBron James and Dwyane Wade and Chris Bosh and their victory over the Oklahoma City Thunder in last year's NBA Finals. They pointed to their Eastern Conference Finals comeback over his Celtics to show all they could offer him.
The Celtics were incapable of giving him what the Heat could. More than 15 years into his career, it wasn't about the money or necessarily the role. Winning was all that mattered.
Boston wasn't built to contend (see their first-round exit and Doc Rivers and Kevin Garnett's attempts to leave) like the Heat were. There was no ring potentially waiting for Allen by if he came back for a sixth term. So he left the Celtics in favor of the Heat.
That Miami also needed Allen was an added incentive. Upon arriving, he wouldn't merely be along for the ride, rather he'd round out a formidable Big Four.
His deep-ball prowess and penchant for draining big shots from the outside was a luxury the Heat weren't afforded. Until this season, LeBron wasn't known as a lethal three-point weapon, Bosh looked out of place beyond the arc and Wade avoided treys like the plague.
Mike Miller was good for the occasional effort put forth in Game 5 of the finals and Shane Battier continued to be money from the corner, but neither of them were Allen.
One easy sales pitch later, the Heat had the future Hall-of-Famer playing in Miami. Landing him began to pay immediate dividends for the dynasty-seeking Heat.
In just the third game of the season, they trailed the Denver Nuggets by one at home inside of 15 seconds to play. LeBron had the ball and attacked the rim like any defense in their right minds would expect him to. Then he did something he hadn't been able to do through his first two years with the Heat—kick the rock out to the left corner where the greatest three-point assassin in NBA history awaited.
Allen caught the pass, went up for the shot and BANG—he drilled it.
Fouled in the process as well, Allen stepped up to the free-throw line and completed the four-point play, giving the Heat a three-point lead and inevitably the victory.
That's when the extent of his value to a team like the Heat was realized. Miami had another big-time baller in the lineup, someone who could shoot them out of tight spots and toward a championship.
Per Kurt Heilin of NBC Sports' ProBasketballTalk, no one in the NBA made more three-pointers with the game separated by five or fewer points inside of five minutes to play in the regular season than Allen.
He added a clutch component the Heat didn't have last season, a dynamic that no one else on the roster was capable of imitating. You can't teach what Allen has, it's just there, as it was for the Heat all season long.
More than eight-months later, Allen is still that same guy. Ask the San Antonio Spurs or his teammates or coach Erik Spoelstra. Better yet, watch footage from Miami's pivotal Game 6.
Trailing the Spurs 3-2, the Heat needed to force a Game 7 or leave the AmericanAirlines Arena with their quest for a second straight title dead. Down by double digits leading into the fourth, doubt began to mount. Could the Heat really come back from this?
LeBron willed the Heat back into the game, but wasn't able to close it out on his own. It was still a two-possession contest with under 30 seconds to play. Pessimism began to take center stage as "fans" began leave.
A LeBron-made three after a missed three made things interesting. Kawhi Leonard went 1-of-2 from the line, leaving the Heat within three. On the ensuing possession, LeBron missed another three, but Bosh was able to grab the offensive board and find Allen in the right corner.
Just as he had so many times with the Celtics (and Bucks and Supersonics) and with the Heat this year, Allen buried the biggest shot of the night, tying the game. The Heat went on to win in overtime and force a Game 7. Now for a second straight year they find themselves one win away from a championship.
Allen was far from flawless in Game 6, going 3-of-8 from the floor for nine points. He also only attempted two shots in that pivotal fourth quarter—both of which he made and both of which were absolutely imperative.
Allen's first shot of the fourth gave the Heat an 84-82 lead, serving as the ultimate momentum shifter. His second, well, you already know (BANG).
In overtime he chipped in four points, including two huge free throws that helped ice Miami's come-from-behind victory. It doesn't get more clutch than that.
LeBron led the charge in the fourth, but the Heat don't win Game 6 without Allen. Sans him, there is no Game 7, no opportunity for another title. Without him, not even LeBron could have saved the Heat from the loss they staved off.
If the Heat win Game 7, they'll have Allen to thank in addition to LeBron and Wade and Bosh. An enemy turned friend, he's helped shoot, helped lead the Heat to where they are now.
It hasn't been easy. Leaving the Celtics wasn't easy and enduring the criticism that came with joining an arch nemesis wasn't either. Perseverance and a sweet-looking jumper have gotten him through, allowing him to make the absolute best of what was a difficult situation.
Under less than ideal circumstances, he's proven to be the perfect fit.