The way I interpreted this was that it was less about (directly) creating more exit flow from SW:GE and more about avoiding creating a log jam in TSL.***
As
@peter11435 said, the potential plan is that "upon opening" (which I take to mean the initial N months when SW:GE is at capacity and entrance is controlled and limited to only the Grand Avenue entrance) the TSL entrance will be exit-only. During this time, only some of the people exiting via the TSL exit actually want to visit TSL. For the rest of the people, it's better for Disney to use the Metroville exit to shunt people back to the "hub" instead of flowing them all through TSL. And in the worst case, TSL itself will be capacity-controlled and so you may not want *anyone* from SW:GE to exit into TSL.*
* However, in this case someone is going to have an aneurism because they are going to be forced to stand in two hours long lines to enter different sections of DHS - SW:GE and TSL. **
** Presumably this won't happen because,
as everyone knows, TSL was a complete failure. /s
*** Note that if you create a log jam in TSL, you *will* impede exit flow from SW:GE.