That’s the regulation in Austria and many other parts of the continental Europe (caskets/outer container required for burials) . And if it’s an above-ground interment, the deceased must be interred in a lead-lined coffin by law. Unlike in US, there is limited available cemetery space and cemeteries re-use old graves after a suitable lapse of time, as it’s a common practice in Europe. The bright side is, people can ”adopt” old Victorian or Gothic monuments and the overall deterioration of the cemetery minimized. In France, they adopted a standard practice of issuing 30-year leases on gravesites, so that if a lease is not renewed by the family, the remains can be removed, space made for a new grave. The exhumed remains (mostly skeletal) are stored in smaller boxes in an ossuary (a chapel on the cemetery grounds built for this purpose). I know most people in US wouldn’t like the idea of burying a loved one in a ”second-hand grave” but in overly populated places such as NYC where they run out of grave space,this option should be considered.