Came down to $/mile, and man-hours/mile.
Diesel locomotives are cheaper to build, maintain and operate. Need more power for your train just stack more together. All are operated by same crew, unable to do that with steam locomotive, a double header needed two crews.
Any cuts that were grade lowered were done for safety concerns, downhill speed.
All this argument over ice and ev. Who's worse on or better for environment. As long as they both run on current tires they are environment pigs. The amount of energy that the however many sets of tires the vehicle uses in its life (raw materials, manufacturing, transportation to and from retail and distribution on front and back side, disposal energy, cost of getting rid of non recyclable content. Tires are a worse environmental menace than any cars ic or ev.