Because that is what you say in Japanese when you start eating but interestingly it doesn’t mean “Guten Appetit” (basically “have a nice meal”) but “I am (thankfully) going to receive (a nice meal)”. While “Guten Appetit” is about others who are eating alongside you, “itadakimasu” is about the speaker.
Did you mean itadakimasu?
Because that is what you say in Japanese when you start eating but interestingly it doesn’t mean “Guten Appetit” (basically “have a nice meal”) but “I am (thankfully) going to receive (a nice meal)”. While “Guten Appetit” is about others who are eating alongside you, “itadakimasu” is about the speaker.