Not necessarily - prices in the region might have depreciated overall, maybe it was built in a market high and sold at a market low point.
The people/company selling it might have had other monetary problems and were thus selling because they needed money and couldn't afford to wait.
If you build an underground house it is probably because you want an underground house, if you then die your heirs might not want an underground house, but to sell it they have to find someone who wants an underground house, thus to make it more interesting to buy they lower the price because maybe someone on the fence about living in an underground house will be willing to give it a try.
The people/company selling it might have had other monetary problems and were thus selling because they needed money and couldn't afford to wait.
If you build an underground house it is probably because you want an underground house, if you then die your heirs might not want an underground house, but to sell it they have to find someone who wants an underground house, thus to make it more interesting to buy they lower the price because maybe someone on the fence about living in an underground house will be willing to give it a try.