It's because, quite frankly, we're fancy.
Or, you know, because it's a thing we do.
We're not really sure, but it's probably for the same reason you write in Roman.
We're a bit of a weird, pretentious crowd, okay?
But hey, at least our writing is interesting.
Want to learn more about why we really write in Italic?
Or how about the other reasons we write in Roman?