Do you understand that many of these publishers do not have the original copy anymore, and may have gone out of business entirely? 50 years ago text was not backed up to the cloud.
They're often books tied to a region, i.e. stories about a local fisherman's life and how they overcame adapting a boat to local feedstock, or the engineering that went into building the local train station. That's to say they can have little value to those outside the area but are still a rich read for locals, tourists, and those who move to the region or have a love for a place. I expect we'll see a concerted effort to organise to get these kind of book sent to regional mueseums for scanning now that people are aware they are actively being destroyed and they realise the timeline isn't how long the book can last.