From observations of our grandkids who have ‘phones, I’d postulate that most teens and twenty-somethings almost exclusively text.
Two possible causes: 1) It maintains the same sort of semi-anonimity characteristic of Facebook or other online social sites (You can always claim that some villain “borrowed” your phone if something “offensive” goes out....) and/or 2) There’s a certain degree of security possible: You can’t be overheard and you can always delete the text immediately after transmission so that nobody (like Mom) can snoop.
I don’t get it when email does the same thing.