Collectors and dealers of the 1930s and 1940s looked at the obstacles to increasing the popularity of US philately and decided that unnecessary complexity was off-putting to new entrants to the hobby. This feeling was created by four things. First, the classic one cent and ten cent 1851 with their different minor plate types being elevated into major catalog number status was felt to be off-putting, creating major rarities (such as Scott #5) where the same type of variety of a more minor country than the US might not even be listed. Second, there were the numerous minor shade varieties of the Nineteenth Century that received major number status. The colors of the 5c 1857 (Scott# 27, 28, 28A, 29, 30, 30A) all had spaces in the Scott album. Many were rare and need an expert to determine them from much more common shades that look very much alike, even to the trained eye. And third, the paper and shade varieties of the Bank Note issues (Scott # 134-218) created many varieties with appeal only to advanced students of stamps. And lastly, Special Printing and official Reissues created many major catalog number rarities that only a very few collectors could afford.
The goal of the simplifiers was to make the hobby more accessible to newcomers. Advanced collectors could continue to look for more specialized stamps but the simplifiers created a series of catalogs and albums and for a few years made some inroads in the hobby and looked like they had created an acceptable way of collecting. The reason that the simplified way of collecting didn’t catch on, in the end, was because of the great increase in the number of US stamp issues that started coming out about 1960 and the increasing appeal of First Day Covers and plate block collecting. Collectors who wished for the simple philatelic life were drawn to these newer collecting instruments, and the idea of simplifying the earlier issues lost its purpose and died out.