It wasn't that it was seen as having no value of its own, it was seen as a value-added feature for the hardware. If you had a Digital Equipment VAX, for example, you got VMS source code on microfiche. That made it easy to write drivers and the like. Another minicomputer vendor provided full OS source code listings as well as source code on a set of floppy disks. With that source available I wrote add-ons to the OS, for a project my company worked on, the result was that the minicomputer vendor was later able to sell a bunch of computers to an international customer, for several years.

Ah, yeah, the "letter to the hobbyists".. he came out as quite a snotty little bastard in that letter. Mind, I work with proprietary software for a living, so it's not that I'm against proprietary software at all. But there are good ways, and bad ways.