3. Adding Burnes unlocks more trade possibilities
Starting pitching depth is arguably the Cubs' greatest asset right now. Even without Burnes, the Cubs' starting pitching mix includes Steele, Taillon, Imanaga, Wicks, Brown and Assad, with other legitimate rotation options like Hayden Wesneski, Caleb Kilian and Cade Horton. This plethora of arms gives the team trade leverage to bolster other parts of the roster that need to be upgraded, like catcher, power hitting, and the bullpen.
Adding Burnes gives you one less rotation spot to worry about and makes it easier to ship out a guy like Wesneski or Kilian. Horton would surely draw the most interest on the prospect side, but moving him could mean giving up a legitimate top-of-the-rotation arm. But a tough move like that might be necessary to upgrade the offense and the Cubs will likely be considering all options going into the winter in wake of the Christopher Morel trade.
Moving a quality starter could also be the difference in the Cubs getting a new catcher. The Athletic's Sahadev Sharma confirmed that the team pursued Angels star catcher Logan O'Hoppe at the trade deadline this year to no avail. A deal like that is going to require a significant haul of players and dipping into the starting pitching depth makes sense, especially if the Cubs sign Burnes.