Santa Fe received the majority of EMD FT Units produced during World War Two due to several factors:
1) The huge amount of war production that was sent over Santa Fe's excellent, mostly double - track line between Chicago & the West Coast.
2) The many miles of Desert Trackage, with poor quality well water, meant that water for steam locomotives either had to be treated ( $$$ ), or hauled in by trains so it could be used by other trains. Before long this process would have gridlocked the railroad in California and Arizona.
3) Not only did diesels do away with the need for water, they also reduced stops to cool brakes and wheels by use of dynamic brakes on long downhill grades. This meant faster running times over the desert lines of Santa Fe.
I too, have not heard of any wanting for EMD FT's by EwePee or Espee. Both railroads had large fleets of fairly modern steam locomotives, well capable of hauling their wartime traffic, and few of the water issues Santa Fe had.