I am a millennial and I grew up with computers. I was taught that it was grammatically proper to use dashes, not hyphens. Microsoft Word (and later, Google Docs) made this trivially easy because you could type two hyphens (--) and it would replace it with an em-dash character. I rarely write in Word or Google Docs these days, but when I do I still do that double-hyphen shortcut.

I think the main reason people are noticing it now is because most writing has moved away from legacy tools like Word. Websites like Twitter don't do that character substitution, so it has become quite obvious when text is being pasted from another place...for example, AI generated content.