There is no "why". It just is! If you ask "why", you won't learn anything.

Hi, this is common to all translations. For example in Lithuanian people say I feel the cold on me but translated into English = I am cold.

P.S. No. It's not translational question. It's about culture. You see, phrases 'Guten appetit', ' Bon appetit' contain word 'appetit' and mean something like 'have a good wish for food', but in english just 'enjoy a food'.