The block editor accesses data through the REST API, not direct database queries. Meta fields require explicit registration to appear in REST endpoints due to security and schema requirements that don’t exist in traditional PHP development.
Unlike PHP where all meta is accessible by default, the REST API requires type definitions, sanitization callbacks, and explicit permissions for each meta field. This prevents accidental exposure of private data and ensures data integrity.
Meta registration serves multiple purposes: defining data types for API schemas, providing sanitization for security, controlling access permissions, and explicitly marking fields as public or private through show_in_rest settings.