At the time, the only choices were "ed", "ex", and "vi". I did use "ed" (and find to my amusement that it still exists on my modern Fedora 40 linux machine). With vi available, a person would have to be crazy or stubborn not to use it.
At the time we were using a variety of serial terminals. Each brand of terminal had capabilities described by an entry in the /etc/termcap file. You rarely hear about this these days, but it can be relevant if you are using a terminal emulator to a serial port or an ssh connection to a remote machine.
I continue to use "vi" on Sun workstations. My habits were entrenched and although other editors may have been available on Sun machines, they were not better, just different, so I continued to use "vi".
The original "vi" editor was written by Bill Joy around 1976 when Bill was a Grad student at UC Berkeley. Bill Joy later became one of the founders of Sun Microsystems.
Since those days, "Vim" has been developed with many enhancements and extensions.
If you have ever seen an ADM-3A terminal, those keys are marked with exactly the left, right, up, down motions. Coincidence? Maybe, but I doubt it.
Tom's vim pages / [email protected]