Grizz, this is just a guess.
Apparatus purchases were delayed during World War II and by 1945 the department was in need of a lot of new rigs. At the same time the federal government had a surplus of pumps that had been ordered for fire protection during the war. These were sold at a discount price to apparatus manufacturers and this helped keep the unit cost lower and reduce the City's total tab.
Many of the new rigs purchased went to the outer bouroughs to replace old 700 GPM LA France pumpers that had been around for years. Even those initially assigned to showcase companies in Manhattan were soon reassigned out across the bridges where pump capacity was less of a factor.
