According to Thinking With Type,
Italic letters, also introduced in fifteenth-century Italy (as their name suggests), were modeled on a more casual style of handwriting. While the upright humanist scripts appeared in prestigious, expensively procured books, the cursive form was used by the cheaper writing shops, where it could be written more rapidly than the carefully formed lettera antica.
But when I see a wedding invitation these days, it's (almost) invariably printed in Italic.
So how did "casual" and "inexpensive" switch to "formal" and "expensive"?