In the summer the warm exhaust from the fridge gets dumped into the kitchen along with heat from cooking. Then the cooling system has to work harder, or if there is no cooling system it just means less comfort and fans running more.

So I have to ask, why don’t refrigerators have a duct so the warm air can be vented outside in the summer?

In the winter I actually adjust the fridge temp to be colder so food lasts longer because the output is beneficial anyway.