They actually showed up on the first scan by the first WiFi-capable device.
Scientists theorize that the first early wifi SSIDs emerged due to randomly-combining network packets in the early "primordial soup" of the internet, over 4 billion
40 years ago. Those which were most successful at acquiring network resources soon evolved into the LANs we see today.(posted on Hubzilla instead of Mastodon because Mastodon's editing UI doesn't support strike-thru. ...or any other formatting markup. for some unknown reason coughcoughTwitterenvycough)