system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a graveyard stay in business after it's full?
gpt
Even after a cemetery is full there are still maintenance costs for things like landscaping and security. Cemeteries have a few ways to keep paying those fees. 

In many states in the United States, cemeteries have to set aside a portion of each purchase for a perpetual trust. The interest earned on that trust is supposed to be enough to continue operating the cemetery once it fills up.

In some places like Germany graves are leased for about 20 years or so. After 20 years if no one renews the lease the headstone is removed and the grave becomes open to a new occupant. Under this system cemeteries are always making sales because graves either open up or get re-leased.

In some places like England they go for double decker graveyards. Some cemeteries will dig a grave deeper so that another coffin can be fit above while still buried.

Not every cemetery is financially successful. What happens when a cemetery goes bankrupt is pretty highly dependent on the specific situation and applicable laws.