I guess the prices are to reflect the convenience of not having to assemble the ingredients and cook it ourselves.
Having said that, I find the prices ridiculous too.
I like to cook and honestly, I have never bought anything premade that tastes anywhere near as good as something I make myself.
You are absolutely correct, many times food items sold here are much cheaper on Amazon or Sam's club.
“The price of light is less than the cost of darkness.”
– Arthur C. Nielsen