Folders were produced after 1958 but the popularity of the TLR & SLR were by far outpacing the demand for them. So I guess you could say that year might have been a turning point.
For most of the last 4 decades I've used SLR's & TLR's. It's only in the last few years I've found a fondness for the folders.
6x6, 6x9 & 4x5 (Crown Graphic) folders that are starting to see some use now.