In exchange for a one-time windfall, the property is maintained in perpetuum (more or less).
If it is so great, get into the business. I don’t see a need to tax the grave.
Correct. Cemeteries need to have a plan to be around forever. That means that once a cemetery is full and no new money is coming in, it must have a large enough endowment so that the interest covers maintenance.
If it also had to plan to pay property taxes for an infinite numbers of years into the future, the cost of each burial would have to be much larger.