Money:

The contract for Eason is actually a 4 year/~112m extension, starting in the 2026-27 season, but Fanspo just doesn't let you do that.

DFS has to be included in the trade because of Base Year Compensation rules. In a RFA sign-and-trade, only half of the new salary counts for the sending team (Rockets) so they have to send out more salary for matching purposes. Meanwhile, because they are an Apron team, they cannot take on more than they send out, so this is a tightrope. The only other player on the roster that works is Adams, and I'm sure they aren't interested in trading him.

Logic:

Houston is stuck between a rock and a hard place with Eason. They either match a poison pill deal from someone like the Lakers or Nets, or they lose him for nothing. Here, they get a volume floor spacer who fits as a 5th starter or a super-sub without having to commit salary into 2030.

San Antonio makes a bet that Eason's improvement from 3 this season is legit, not a flash in the pan. He slides in nicely at the 4, and they play a starting lineup of Fox/Castle/Champagnie/Eason/Wemby. His size and defense also gives them some flexibility in 2027 if they have trouble in negotiations with Champagnie, who has earned a big raise off one of the best value contracts in the league.

Taking on DFS seems like an anchor, but his contract is only guaranteed through next season, so if he doesn't improve next season off the Spurs bench, they can buy him out next February or cut him in the 2027 offseason with no problem.