Did The USA (Pre-1950) Print Stamps For Collectors Only?

Commemoratives have never been "primarily to frank mail". Regular issues exist for that. And there would be no problem printing all the regular issues necessary if the USPS had wanted to do so. People used commemoratives because they were there and/or because they liked them, but if they were not there then they would have used something else. That's why the pre-1920 stamps which are popular and so are expensive but they are generally easily found; nearly all the post 1920 mint stamps are available by the ton as we speak. Of course commemoratives are political, they always have been; they are a form of national propaganda, as they are for all nations. The attitude was clearly "as long as they were being printed anyway they might just as well make a statement". There is no question of that being the intent, but without the collector boom it might well have stayed at one set every 3-5 years, or possibly even longer. Hence the media alerts for new issues, and the FDC availability, and the Philatelic Window in Washington.