>>19523183this is because they often have multiple cameras on the one person and are doing the same scene over and over again.
There needs to be consistency, because often times the director will use two pieces of two different takes and edit them together to complete as a whole.
If the actor eats a big mouthful, then they will consistently need to eat the same amount each take, and they'll get full.
Also, food can get in the way of delivering a line, and ruin the whole take. Which is why characters seldom eat when food is in front of them, and just play with food using cutlery
