What's that wild intuition of underscores???
Also, why would you ever read it as a regex in a human /text/ markup language?
Surrounding text with underscores to indicate italicization is intuitive to anyone who is familiar with that convention.
Personally, I find surrounding text with forward slashes exactly wrong for italicization, because I mentally apply a skew-transform to the text to make the slashes into vertical lines, which leaves the text itself slanted in the wrong direction. Backslashes would make more sense, and also avoid looking like regular expressions. But literally no one uses that convention and we do not need a new one.
Also, this /convention/ already exists and used, despite its low popularity (eg orgmode or Bear note app), so you're also literally wrong here
Also, intuition is "understanding without conscious reasoning," so remembering a convention IMO counts.
Consider e.g. parental intuition of noticing subconsciously it's too quiet and immediately going to find out what the kids have done.
For UI, consider the floppy disk icon often used for 'save' - it's considered intuitive because the vast majority of users already recognise it without having to think about it, even if they've never had a system with a 3.5" drive themselves.
On the other hand, if you know that _ is __underline__, - is --strikethrough--, then you can acquire knowledge (guess) that / is /italics/ because the principle is the same - formatting text follows symbol's shape (though it's not a perfect mach since / transforms text, not adds new symbols unlike _ or - ). But that's still intuition (* for bold would not fit here)
The other bad analogies don't help resolve it, so best stick to the topic
Plus underscores get used -lots- of places for italics; I've yet to see the / form in the wild.
A markup language being (as here) used for technical purposes can easily be interpreted according to geek writing conventions.
Em is just another bad term - which of the emphasis styles do you mean?
Re popularity - so what? How does widespread bad turns into intuitive good?
Bear notes used / for italics, also Orgmode (is that geek enough for you?)
You have you know the fact that actual underlining had been traditionally used as a substitute for italics in hand-written and typewritten papers.
As in, in a citation, when you give a title of a book, you underline it, unless using a word processor with fonts, in which case you use italics.
Learned this in high school.
