[gamblor956]

A worker coming in sick can be a safety violation if they don't wear the appropriate protective equipment (generally gloves and a mask). Picking food of the ground is a safety violation that could get a restaurant shut down, and moreover would open the restaurant up to civil torts. A restaurant is not going to risk permanent closure to save a few cents on food that falls to the ground, especially not in places where they grade restaurants on food safety.

As for using leftovers: this will shock you, but a large portion of menu items in even fine establishments use leftover items (that were not served to customers). Soups, stews, curries, etc., generally involve perpetually renewed bases, where the previous days leftovers "seed" the new day's mix. The meats in pastas and other starch-heavy dishes are usually trimmings from entrees in which the meat is the star. Meatloaves in restaurants always use leftover meats from the day before. Nearly all breads in bakeries involve the reuse of the sourdough starter, and indeed the concept of sourdough itself is premised on the reuse of the the dough.