Because the line of logic goes like this:
1. The Braves are projected to be a 70 win team before any FA signings, and probably 75 after they added Colon, Dickey and a catcher like Castro or Mac.
http://www.fangraphs.com/blogs/instagraphs/come-look-at-2017-projections-already/
2. This 75 win total projection includes a full year of Folty, Swanson, Inciarte, and 400 PAs from Albies.
3. Any trade for Sale will undoubtedly subtract from those 75 wins because the return will have to include at least 2 of those 4 young players the team is relying on just to reach 75 wins.
Nobody other than Braves fans think Sale could be had for any package that doesn't include 2 of the guys I mentioned in point 2. If they could get Sale for a package centered around only Inciarte from that group of 4, I would agree it could be a wise move.
However, there is no way the best offer the ChiSox will receive for one of the most valuable assets in the game is Inciarte and a handful of non-elite prospects. If that's the best offer they get, they will just hold onto him until the deadline.