From what I have seen, it's not common to find "unaltered" K&T wiring. A house wired to what was common and needed 70+ years ago couldn't meet the needs of what is minimal in homes today. Today homes need more outlets, more capacity, more fixtures, etc. Things like a simple window AC unit that you can buy for $100 didn't exit then. So, it's common for these K&T systems to have been added on to, expanded, partially replaced, etc with a variety of more modern wiring. And a lot of that work was done by the homeowner or some hack so that you have dangling splices, no junction boxes, etc.
I think it's unfair to accuse the insurance companies of "redlining" because they have concerns about K & T wiring and demand that they prove K&T itself is the problem. If it is in fact unaltered and still used as intended, it may still be safe. But in practice, it's rarely left alone and still used the same way. Personally, I would not trust it in any home I was going to live in. Is that redlining?
Would it make you happier if instead of saying they won't insure homes with K&T insurance companies instead said they won't insure homes older than 70+ years if they still have the existing wiring ?
Bud, you jump on Bob for not giving you any relevant authority or data. In the case of insulation around K&T, he has showed that the NEC doesn't allow it. Yet, when he does, your response is many jurisdictions allow insulating around it. I don't know about you, but I'd give more credibility to the NEC before the local electrical inspector, building dept, etc.