Why the Phoenix Suns do it
Phoenix has been one of the worst franchises in the entire association since they traded Steve Nash. They have building blocks in Devin Booker and Deandre Ayton. They have capable wings and are employing Ricky Rubio as their lead guard. However, despite a fast start, they find themselves once again as a cellar-dweller in the Western Conference.
In this trade, Phoenix would grab a former All-Star big man who can pair better with Ayton than Embiid while providing playmaking and allowing Booker to sprint around the floor on offense. His biggest impact on the court would be helping to tighten and position everyone on defense. Horford has long been a stalwart on that end. Furthermore, Horford would immediately take over as the elder statesman in the locker room.
Sending Bridges back to the team that provided them the young wing is both interesting and fitting. They will push back, but they need a veteran to help push them forward. The franchise has been complacent for too long. Aron Baynes has proven to be their most stout defender but will always be a strange fit next to Ayton. Ultimately, Horford is a big move that expediates their competitiveness.