The database maintenance is a multi-step operation, including:

-       it will perform actual purge of model data

-       it will maintain the database tables and indexes

-       it will maintain the search index

The database purge of deleted models is limited to a maximum of 2 hours per database maintenance execution. Therefore, if you have not deleted / cleaned up your models for a long time, it will take several database maintenance executions to purge all deleted models.