Oh yes in the 1960s all "lab" grade electronics like power supplies, oscilloscopes, whatevers, came with thick manuals with schematics, part lists and theory of operation as well as the basic user manual.
That's still the norm for many Amateur Radio products. What is missing from many products supplied by the big name manufacturers these days is source code for the embedded MCUs.
Many radios and test equipment used to be available in kit form too. But that has gone away since the advent of surface mount technology. Most Amateurs don't have the equipment, patience or eyesight to do SMT at home. Besides, pick and place robots will assemble a circuit board in minutes, reducing labor cost to a few cents per board. So, instead of saving a bunch of money on hand-built hardware as it used to, it actually costs more to offer kits than it does fully assembled boards. The technical support costs for kits is pretty high.