Timeline for Ice House + Railcars - Model Railroader Magazine

If you want to read a history of reefer operations, get the book "The Great Yellow Fleet", by John H. White.

Model railroaders seem to want to put an icing facility any place there is an industry that uses reefers.  The ATSF, which owned one of the largest reefer fleets in the US (SFRD) only had 27 icing stations and ice plants on the system.  PFE which was a combination of the UP and SP only had 51 ice plants and stations between the two roads.

According to the above book (p. 126), there were about 124,000 reefers in the US in 1955, of which about 5000 were insulated boxcars (RB cars) and about 700 mechanical reefers (RP cars).  By 1965, there 108,000 reefers, 31,000 of which were RB and 10,000 were RP.  In 1970 there were 115,000 reefers, 54,000 were RB, and 21,000 were RP.  By 1975 out of 108,000 cars, ice reefers (RS) had shrunk to 13,000 cars, with 69,000 RB and 27,000 RP.  In 1980 the reefer fleet had shrunk to 88,000 cars and only 2000 of them were ice cars, with 62,000 RB and the rest RP.

If you look at the data, what killed the ice reefer wasn't the mechanical reefer, it was the insulated boxcar (RB/RBL).  It could handle loads that just needed to be kept cool, while the mechanical reefers handled the stuff that needed to be kept frozen.