Sometimes they can, sometimes they can't (i.e. PUB)
People really don't like flying on T-Props, and then you add on poor performance, poor service and a high cancellation rate like GLA had in the midwest and the traveling public will drive or drive to a bigger airport.

Add in OO has all of United's network to connect people in Denver, like Envoy has all of American's network in DFW.
There is a staggering difference in the number of people that drive to GCK to connect through DFW relative to the number of people in Dodge City that simply want to go to Denver.

There were very well populated areas with very poor ridership simply due to GLA. Envoy has boosted ridership in some of these areas to unimaginable levels.