The other issue is that the portion of its fleet that it would have to dedicate to the route just means it wouldn't make sense. It would be purely for O/D traffic and to be competitive it would have to more that just two flights a day which means more aircraft, more mainline aircraft and very little benefit.
DL is saying you can fly us out of SFO to ORD, just connect in SLC or MSP.
If you look at their other ORD flights they basically go to hubs or mini hubs, same as SFO.