copyright prohibits (as in reserving exclusively to the copyright holder) plenty of activities that are essential for users to control the computing performed through the software. without a license that formally granted permissions for these activities, a copyright holder could selectively target users who choose to exercise their essential freedoms. that wouldn't be safe nor desirable.

since we had to learn to use licenses to grant required permissions, we also learned to grant just enough permissions as to enable users to control the software, but not enough for intermediaries to lawfully take freedom away from downstream users.