Why do japanese grocery stores throw out the prepared food at the end of the day?

Question:

Is the food not good if it's not eaten in the same day? Just wondering because I bought something yesterday and I haven't eaten it yet, is it still okay?

Answer:

It is still OK for a couple of more days as long as you keep it in your fridge.
But not more than 4 days. OK?
I have survived by eating thrown out food for the past 20 years.