Most emails are unencrypted. And indeed, in the medical profession, they were widespread. Nothing can protect from the sender putting in the wrong number or email address. I’ve received some seriously sensitive emails not meant for me because the people made typos and the recipients had the same family name as me (not sure how the email server decided it was close enough and delivered them to me).
I’ve also read for some businesses, it was critical to get an instant receipt that the fax has been properly received.
Now, I’m not defending using obsolete fax machines, it just had one advantage over email but today there are much better alternatives and dedicated platforms.