Surely once you have corrected subsidence, the cost of home insurance should plummet, as the problem has been fixed for a century. The reality is much different, with premiums usually surging after a claim.
My parents live in area that is a coal mining district and subsidence is common. Even if the foundations are made safe, there is a higher risk of it returning, hence why premiums are higher and also new home guarantees are minimal. It's the same with damp, even if you have a home damp proofed it can return, so the risk is still higher.
Subsidence increases premiums because claims are likely to increase. During times of the year when buildings are exposed to adversity cracks and other structural challenges increase. The insurance industry is not in the business of profiting a person but rather to make a profit. But it doesn't sound like best practice to increase premiums when your customers are vulnerable.