Perhaps this varies by region? I don't know anyone that buys burgers in a packet. They buy ground beef and either make patties or balls (for smash burgers).
Those are thin enough I wouldn't think to stick a thermometer in them... it would be too hard to get it in the center and not out the other side, and it's pretty easy to get a sense of doneness from the outside (or cut into one and see). Steaks, depending on who's eating and doneness preferences, thermometer is nice. Roasts, almost certainly.