The way I think of it is that GPL (and the precursor the GNU emacs license) was created when distribution was primarily via magnetic media or downloads and hard

The way I think of it is that GPL (and the precursor the GNU emacs license) was created when distribution was primarily via magnetic media or downloads and hardly anyone ran software which wasn't local (BBS software excluded?). Which meant that as soon as you distributed GPL licensed software you also had to adhere to the license of sharing your improvements in source code. Then when the internet through the web became popular you could use GPL software without distributing it and many use cases which didn't exist previously for the distribution options in GPL just didn't create the intended effect where users who changed the software and distributed it should also share their changes. I would argue that AGPL didn't redefine what distribution is, but the capabilities and the use of the web redefined what distribution is, through software as a service. AGPL was an attempt to align the license with the original intent of GPL, which was to say that if you redistributed the software and change it, share your changes.