The Atlanta Hawks weren't in a great position to begin with.
Al Horford had played every single game of his career in Atlanta and he absolutely loved the city. That's about where the list of positives ends for the franchise. The Hawks are coming off an unimpressive year, after their superb season two seasons ago, and traded Jeff Teague on draft night. A makeover was certainly in the works, having traded their All-Star caliber point guard away. That alone would make Atlanta worse, enough of a reason to explore other teams. Then the front office running the Hawks shot themselves in the foot.
They gave Dwight Howard money. It's hard to even get started on why this was such an awful idea.
The Atlanta Hawks offered a starting center a deal before they secured their own All-Star center, whom they supposedly wanted to keep so badly. It's not a good look. They essentially brought in Horford's replacement before receiving official word from Horford that he was walking. And even if Horford was to stay, the issues compound. Horford has been most effective in his career at center. Pairing him with Dwight Howard would not be the most effective way to win games. To further worsen things, not only did they sign Howard before Horford made his decision, but they signed Howard within hours from when Horford was scheduled to meet with the Boston Celtics--who were already a better situation for him.
Fit & Stupidity
Paul Millsap was Atlanta's best player last season. Millsap is a position-less forward who spends a lot of time at the 3, but is more than capable of playing the 4. Millsap is clearly a better fit alongside Howard than Horford is. Howard's signing also rendered the Hawks incapable of offering Al Horford a max contract, which all other teams would. And so, in a foolish last minute scramble to try to retain Al Horford, the Hawks shopped Millsap around to try to create the cap space needed to give Horford a max contract.
This was dumb in so many ways. For starters, this would have never been an issue had they not signed Howard first. Secondly, trading Millsap--for virtually nothing since they couldn't take back too much money--further degrades the talent of this already mediocre team that had taken steps back before having traded their All-Star point guard (and their best player had they actually traded Millsap).
The only thing the Hawks had going for themselves was the fact that Atlanta had long been Al Horford's home. In signing Howard, they failed to show the necessary respect to their star center. In attempting to trade Millsap, they would have made the team even worse than it already was (while devastating Paul Millsap in the process, by making him feel like merely a pawn).
A report was made early Saturday that the Washington Wizards and the Boston Celtics were the front runners to land Al Horford. That report wasn't inaccurate, but it was missing a crucial piece of information. Boston and Washington were the frontrunners merely among teams that could steal Horford from Atlanta.
As reported by the Hoops Inquirer, Washington was never really capable of stealing Horford. The frontrunners were actually Boston and Atlanta. The Hawks truly hurt their chances after the Howard deal, but a source with knowledge of the situation told the Hoops Inquirer that Atlanta's chances were still very much alive towards the end, although just barely. Having played in Atlanta his whole career, leaving the city he had grown to love wasn't something Horford was too fond of.
Washington was the back-up option. Should Boston somehow fail, the Wizards intrigued Horford enough to gain his interest, due to the talent of John Wall and Bradley Beal. However, like Atlanta, the Wizards had also taken steps back in recent years, having not even made the playoffs last year. While Washington's re-signing of Beal is a decent sign, whether he can play a full season yet is still in question.
According to a source close to the situation, Boston didn't have to do much to impress Horford. Horford was extremely impressed from the outside as is. The key factor that appealed to Horford was the culture. Boston's pride and demand for winning was very appealing to the All-Star center. It's a culture like no other, Horford admired. In fact, Boston's Kevin Durant aspirations did not matter at all to him. Their assets and ability to land another star, in addition to Horford himself, was very assuring of the organization's future. However, signing Durant--an unlikely task as is--was not vital to Horford's decision.
Boston's progression and growth every year under Brad Stevens was well-noted by Horford. A clear upgrade at the center position puts Boston that much closer to the top of the Eastern Conference, as everyone out East tries to dethrone the Cavaliers. Ultimately, Washington did not have much of a chance in the sweepstake. Atlanta was holding on to a thread after signing Howard, only being kept in the conversation by a fear changing scenery.
For that reason, Boston would go on to win, without even using Tom Brady.