More people now get cremated in the U.S. than buried. This is compared to 1980 when less than 10% of dead people in the U.S. were cremated. The reasons include much lower cost, more religious acceptance of cremation, and a more mobile population that are more likely to move away from a hometown family burial plot. In South Korea, almost 80% of dead people were cremated, including 99% of those that died in their 20’s.
Burial plots already generally are offered for resale at much lower prices than the retail prices a cemetery offers. Even then, they aren’t particularly easy to sell and many plots stay on the market for years. Think about someone who inherits a plot from a parent that didn’t end up using it or someone who buys a plot in Buffalo, only to move away to Albuquerque with no intentions of ever moving back. To them, the plot may have no real value.
Its not like inheriting a house or being unable to sell it when you get a job transfer. In that case, you can still rent the asset out and generate some income. The burial plot just sits there and generates no income for its owner. Combining that with a declining percentage of people who even get buried, and you have a supply/demand mix where the demand is definitely going down.
Burial plots in some areas probably will become worthless or close to it. These include plots in bad areas and in declining towns where people are leaving. However, there will probably still be some type of demand for burial plots, even if only 10% of the population gets buried. Someone may just want to get buried in California not too far from the beach, and your burial plot could end up becoming their home by the beach that they could never previously afford.