Isn't that survivorship bias?
Processes that never improve yield are abandoned
Processes that never improve yield are abandoned
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).
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.