Why few of my contacts were not deleted?

People in CRM can only be deleted by owners, CRM Admins and the Account owner. However, there are few exceptions when they cannot perform this action.

Conditions when a Person won't be deleted from CRM:

1. If a person is associated with a deal in CRM.
2. If a person is associated with a Project in PM.
3. If a non-admin, who's not the owner tries to delete a Person. 

If you still want to delete a Person, remove the association with Deal/Project and then delete the person.

Learn more about CRM Permissions here.