I don't know where you live, but this is not the case worldwide. I have heard tell, yes, of places in Germany or somewhere else in Europe, where it is customary for a family to pay installments/subscription for a temporary grave, where the remains are left to decay down to bones. And then the remains are extracted and placed in a more compact crypt or charnel house, and the family stops payments on the full-size grave, which can then be reused for other occupants.

But in my part of the world, remains are "permanently" housed in cemeteries, crypts, colmbariums, etc. The family pays once for the interment and the plot. The cemeteries themselves are self-sustaining businesses which typically have a large endowment so that they can operate in perpetuity, with assurances of maintenance and upkeep far beyond any family's ability to sustain payments.

I think we can all agree that it would be absolutely absurd to expect families to continue paying in perpetuity for a burial place for their ancestors. Can you imagine the exponential financial burdens that would result?!