When can an object have an owner and no controller?
Only objects on the battlefield or on the stack have controllers - everything else is only owned


  108.4. A card doesn’t have a controller unless that card represents a permanent or spell; in those cases, its controller is determined by the rules for permanents or spells. See rules 110.2 and 112.2.


But there are many cards that can affect cards in hand, library, graveyard, and exile - for those cards, choices are made by the owner because nobody controls them.