Let's start with the Blinding Flash of the Obvious answer: These units are obsolete. The E-9s Union Pacific and the F units BNSF use for executive service have been rebuilt. They have -2 or better electrical systems, and in the case of the UP E units, they are re-engined with the 645 series Diesel.The secondary answer, especially compared with modern hood or hood/safety cab construction, is that they are expensive to build. Streamlined Diesel units of this era used a form of truss construction where the skin and frame gave to the strenghth of the carbody. Modern units, including all hoods as well the FP45, the SDP40F, and the F40, rely on the frame for strength, the engine compartment and crew space is all weather shelter.
Finally, in the case certainly of EMD's E units, their wheel arrangement is A1A-A1A, meaning powered-idler-powered on each truck, vice C-C (3 axles, all powered) or B-B (2 axles, all powered). They have somewhat reduced starting tractive effort.
John
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The City of Saint Louis (UP, 1967) is still my standard for passenger operations
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