This is not true. The UK has a £3.85 meal deal that is a sandwich + a snack + a drink. It's hugely popular.
Germany has the Döner Kebab, it's now about 5-9€, but the have cheaper options available too. Again, hugely popular.
I'm sure most European cities have these.
A sandwich, snack or Döner Kebab is not a full nutritional lunch.