CNS&M had a number of handicaps that ultimately killed it.
Most importantly, they fought CNW and MILW tooth and nail for CHI-MKE traffic and northerly suburban traffic. It was always a catfight between CNW and MILW for this traffic, and the CNS&M wound up the biggest loser. Contrast this to the CSS, where PRR and NYC essentially gave up on the CHI-Gary-SB market after 1926 when the CSS was rebuilt and re-equipped.
CNS&M never had a deep-pocketed parent to help them through the dark years, CSS had C&O.
CNS&M had to access downtown Chicago via CTA tracks, which was congested and also limited train car length to 48'. That means much more repair and maintenance cost per seat mile.
CNS&M also had only moderate freight traffic. There were no on-line steel mills or power plants (at least of appreciable size, there were a few industrial-sized on-line power plants). CSS freight traffic subsidized the railroad from 1950 to 1967, when the C&O took over.
Finally, I believe the CNS&M was owned by a quasi-hostile owner. I don't remember this exactly, but I believe the NYS&W had an ownership position, and CN&W had an ownership position in NYS&W, so the C&NW director on the NYSW board was the hostile element, leading NYS&W to prompt a CNS&M shutdown.
If you want to ride the CNS&M, there are plenty of restored cars running around midwest trolley museums. Also, the CTA operates the Yellow Line over ten miles of former CNS&M routing.
We're leaving out the third sister of the Insull interurbans, CA&E. They folded seven years before CNS&M. This was a sad sack of a railroad - almost no freight traffic, and they had to compete with three roads for passengers - CB&Q, MILW, and CNW. They had to compete with five roads for freight traffic, also including IC and CGW. When the CTA rebuilt their Congress Street line in the median of the Eisenhower Expy, the CA&E gave up their trackage rights to downtown in favor of a "Change at jamaica" style transfer at Forest Park, where riders could pay another fare and ride CTA downtown.
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