My parents lived in Tulsa when the Cimmaron was in development. In fact my parents saw the town of Keyesport (and some others) before they were forced to relocate for the lake.
My father said the Cimmaron was really for Oklahoma State University. The upgrade of the rest of the route to Enid came later to support Vance AFB.
As for the Hugo-Durant question, my armchair thought is that at the time Houston was a major port at the time and it made sense to increase capacity. Also I would look at when the Arkansas-Verdigris waterway was built for the Port of Tulsa and Catoosa.
As for Durant, and the traffic pushing north from Dallas, I assume that NAFTA and increased Mexican trade has caused traffic to increase to KCMO. Something not anticipated in 1954.
The McClellan–Kerr Arkansas River Navigation System opened for barge traffic in 1971. 17 years after the Hugo route was put together.
It was chiefly done as a quid pro quo for approval of other turnpikes. As mentioned upthread, Gene Stipe was heavily involved and he controlled enough votes to kill it otherwise.
There have been various efforts over the years to ensure all parts of the state were connected by a turnpike. Woodward-OKC, Altus-Elk City, etc. Most ended up as 4 lane highways (OK6, US 270). the Indian Nation ended up as a turnpike because the Little Dixie crowd didn't want to wait 40 years.