This line really stood out to me - I was aware early semi yields were poor, but this poor? Was this par-for-the-course for technology at that time, or was this bad even by 70s standards? What do typical yield numbers look like today?
Processes that never improve yield are abandoned
For a glimpse at how they do things, see this fascinating talk: https://www.youtube.com/watch?v=NGFhc8R_uO4
You'd be surprised. My personal knowledge of one major fab is that they have policies such as regular rotation of employees which make it difficult to maintain institutional knowledge. I have heard complaints from multiple people of their teammates and managers "winging it" to think it's isolated incidents.
Nowadays, when a new process enters risk production, yields are expected to be sub-optimal (I think I read that some of the recent stuff TSMC was making for Apple was below 50%) but it's an economic imperative that they improve (and they do). Abandoning a process once you've built an assembly line would be an existential crisis for a high-end semiconductor company, given the billions of dollars it costs to get to that point (which is a big reason why Intel has been between a rock and a hard place for the past 5 years or so).
Growing just silicon crystals was still difficult let alone on sapphire--3 ionch wafers were the norm. Lithography was contact so degrade your masks over time. Threshold voltages had poor control. CMOS chips were very susceptible to ESD punchthrough. Latchup was murderous (SOS helps cut this down greatly). You had purple plague. I can go on and on.