to me as people have a lot of bitcoin they do not like to keep them in one wallet as there is always a chance of hacking the key therefore they use multi wallet instead of one wallet.
i agree with you and i think its good idea if someone try to hack bitcoin so they can not hack all bitcoin from one account and i think its so good idea to divide your all bitcoin on multiple account and i also prefer that its really good way to save your bitcoin from hackers.