Memphis is about to face a roster crunch over the next 2-3 years as they won’t be able to pay all the 10+ good young players they have on their roster. Even though they’re winning right now, it always pays off to start consolidating your assets before they become expiring contracts who everyone knows you can’t/won’t pay (see: Reddish, Cam). A move like this allows them to turn 2 very good players into 1 great player on a much longer contract, which means 1 more starter they won’t have to worry about losing as they figure out how to pay Ja and Bane.
Toronto has the opposite problem, their starting lineup is great but they have no depth. This trade helps them stockpile more young players and assets. Brooks is obviously having a great season and would give their starting lineup a bit more playmaking. Xavier Tillman is stuck behind a ton of other bigs on the Grizzlies depth chart, but looks like a guy who could be a very good (and very cost-effective) starting center on a team with more opportunity. With Achiuwa not really cutting it so far and Siakam being better as a PF, this would make them significantly better now and going forward.