If it helps with your understanding land types are what give the ability to tap for mana on the relevant lands. The text boxes on basic lands is actually empty, and cards like stomping ground only have the enter untapped clause. The reason the land can produce mana is because it is a land and has a basic land type. If either of those stop being true it can't produce mana anymore

Different card types and sub-types have different rules implications so they are each in their own category. If you turned an artifact that's an equipment into a creature that would also not count as a creature type for zookeeper