Metaspace, since JEP-387, reclaims memory after purging and returns it to the Operating System. We added a MetaspaceReclaimPolicy switch to control this behavior. Among other things, we allow reclamation to be completely disabled (MetaspaceReclaimPolicy=none). This was a fallback mechanism in case the JEP-387 metaspace turned out buggy. 

But post-JEP-387 metaspace is pretty stable, and has been in the OpenJDK since Java 16, so this reclaim mode is not needed (see also CSR JDK-8302130).

This mode makes backend coding and test coding more complex, since arguing about how much memory we expect metaspace to have committed is difficult if we don't reclaim. Removing this mode would remove some of that complexity.