They'd created Arpanet in order to log onto remote computers. E-mail was the killer app for 20 years, until the Web came along.
Some people still consider it networking's killer app.
The goal there was to fill the building with computers, not to fill the nation with computers. Being the network guy, my job there was to connect the computers in the building. I guess it was the world's first laser printer. We had to build a network for megabits per second, to feed that computer, to keep it running. So connecting this laser printer to the in-house network was the pressing problem.