Which is convenient, since Disney-the-company will never die, and need not have any actual human connection to Disney-the-man-who-actually-created-the-intellectual-property. So it provides a mechanism for people other than the person who created the work or his heirs/designated beneficiaries to profit from his work forever.
Defining "creators" as actual human beings provides a useful marker for how long a copyright is useful: at some point that human dies, and then at some point later his heirs die, and then at some point later their heirs die, etc. So you can look at the question in terms of how many generations should have a monopoly on their forefathers' works. Defining corporations as creators takes that marker away.
Copyright protects the works of natural persons, not corporations. It protects the individual creators when they make a work; they can of course immediately assign their rights to the company, eg by a work-for-hire arrangement, but [co-]creators are always natural persons.
