Why hasn't the KCS looked at a new route to St Louis

And im talking about the ex Rock Island line from Kansas City to St Louis. It doesn't have to cross the Missouri River and it's faster. Just wondering why they never looked at the route.

Four reasons:
1. They already own the former Alton line, and have invested in it and its St. Louis connections.
2. They don't own the former Rock Island line, and most of it has been embargoed or abandoned outright.
3. There were always more potential shippers on their current routing.
4. Neither route will ever be as fast or as competitive as the Union Pacific's routing.

Simple: There are NO St. Louis lines for sale. The KC-St. Louis line is a leftover from the abortive Chicago, Missouri & Western, who was a reincarnation of the old Alton. When the CM&W went bankrupt, SP took over the St. Louis-Chicago segment, while the St. Louis-Kansas City line was reorganized as the Gateway Western Railway with the help of the Santa Fe. With the BNSF merger, all of ATSF's interests in the GWWR were divested, and KCS had long wanted this route (the ICG merger was held up due to KCS demanding the Alton). While the Chicago-St. Louis line is owned by UP, much of the traffic SP poured over it was transfered to UP's C&EI line, leaving Amtrak and KCS (via trackage rights) as its primary users. Hypothetically, KCS could buy the ex.WAB line from NS, but while it is an outcast, and doesn't have substantial interchange traffic, it is a valuable asset, being used for RoadRailers and also as the second fastest St. Louis-KC route.