They made their money reprinting the same volumes for decades. Siddurim such as Shilo, Tikkun Meir. No new works came out since shortly after 1960.
The advent of modern computer driven printing/publishing made their library of set type obsolete and worthless.
The baby boom requirements of Hebrew and English texts for non-frum afternoon and Sunday Hebrew schools kept them viable until the late 70s.
They could not compete with the computer based type setting of newcomers such as Art Scroll.
Finally, they fell victim to cheap overseas printing and the availability of many resources on the internet.