These tables are available by default in a ServiceNow instance because they are part of the core platform and are used to store essential data for users, incidents, and tasks. The other tables are not available by default, but can be created or activated by installing plugins or applications. References1: Tables & Dictionary - Frequently asked Questions (FAQ) - ServiceNow2: ServiceNow - The List of All Tables (sys_db_object)3: How To Set A Default Field Value in ServiceNow? - The Snowball