Why not Diesels earlier?

Why were the railroads decades behind highway users in going from steam power to internal combustion engines? I know IC requires less scheduled maintenance and less infrastructure. Were the early IC engines not powerful or reliable enough? Was refined oil that much more expensive than coal?

both large enough diesel engines and electrical gear large enough to handle that horsepower were simply not made in size that fit in locomotive of that time.

Also, railroads serving the coal regions were reluctant to be seen doing anything that might hurt the coal industry. The Pennsylvania, for example, far from adopting diesels when they did become practical, went to extraordinary lengths to develop new designs for steam locomotives to prolong the use of coal for as long as possible, as did the Norfolk & Western and Chesapeake & Ohio.

Diesel engines of the required power were just too large, and too heavy. The technology advanced in the 1930s. GM's 2 stroke line of engines were in the forefront of high power to weight, as a prime example.