This is exactly the reason. Big-name insurers trade in volume business. The more they standardize the product, the cheaper they can sell it - not a whole lot different to any other industry. That's not to say they don't attempt to have sophisticated pricing models that ingest all kinds of underwriting data points, but there are costs to that complexity too.

There is a broad market in specialist insurance which caters to the non-volume cases. It just costs more because you have to expend more effort-per-sale (and of course because non-volume also tends to mean that the risks genuinely are higher - e.g. homeowners with prior subsidence claims).