[Phil] I suspect it's because the Italians would never take cheap bread and squish it between hot plates to make it palatable, let alone consider it a delicacy. It's a rather recent lunch-comestible-vendor's invention.
[pen] I used to get my lunchtime panino/i in a food court in Dublin, cooked by Italians. They had a choice of 4 each day, and were various combinations of parma ham, bresaola, aubergine, olives, mozzarella, basil, pesto, sundried tomato etc. Always delicious, and great with a large espresso.