It may help to remember that version 2 of the GNU GPL was published in June 1991. According to Wikipedia, only 11% of people in the developed world had internet access in 1997, and I can assure you that in 1991 it was very much fewer than that. Most university research users had it, though often not undergraduates; outside academia, it was really quite unusual to find access either from work or from home.
You could in those days still buy all the GNU software on tape, from the FSF, and I have personally worked for companies that chose to do that. Since those weren't cheap, but the software itself was free, many people would snarf a copy from someone else, who'd got it from someone else, who'd got it from their milkman (joke); or you'd call a friend who was doing a PhD at somewhere with a good connection, and they'd FTP down a bunch of sources and stick them on a tape for you; or you'd get a floppy from a friend, which had enough space for the source you wanted, but not much more than that (1.2MB on a good day, until those super-wizzy three-and-a-half inch discs came in).
Under those circumstances, it was quite common to unpack source tarballs full of
.c files that started
Copyright (C) yyyy name of author
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
but which contained no actual copy of the GPL, because it had become detached at some point in the delivery chain. If that happened to you, and you weren't familiar with the GPL - which was a pretty revolutionary licence when it was written - then you'd need to know your rights and obligations, which meant getting a copy of the GPL. If you really couldn't get a copy anywhere else, you could get one by writing to the FSF, enclosing an SAE or International Reply Coupons if you were well brought-up, and they'd send you back a copy of the GPL. It was a public service they offered, to help spread this revolutionary idea of copyleft.