In my area the houses on at £1million+ are very often abysmally presented (and this is the top end of the market here). A very large percentage of them appear to be owned by elderly people though, and don't seem to have been updated for several decades.
I wonder if the lack of effort is simply that they don't want to sell, but are having to do so to pay for care. There just isn't the incentive to market your house as well as possible when it's all going on care home fees anyway.
It may also be generational differences in taste too though; the vendors probably haven't considered that the much younger buyers will look at the house and think it desperately needs a new kitchen, bathroom(s) and that every single surface will need to be replaced/decorated (flooring, walls, etc). They may well think their houses are beautifully presented.