what's puzzling is *why* the routing through DEN is so expensive? a one way fare BWI-DEN-HOU is $887 while it is $168 BWI-ORD-HOU

Last month I rerouted ultra cheap ticket during the flight and had no problems making essentially any change I wanted (ultimately back to BWI where I started from). I'm just wondering if this will work because it's something like 3000 miles each way