Why can’t soups with starches, pasta, flour, or dairy be canned?

probably that they have a short shelf life.

The dairy will spoil, and the starches will absorb the liquids and taste bad.

I love campbells cream of mushroom soup.. it has starch and creams in it.. found this online from campbells,,,,,,,,,,,,,, INGREDIENTS: WATER, VEGETABLE OIL (CORN, CANOLA, AND/OR SOYBEAN), MUSHROOMS, MODIFIED FOOD STARCH, WHEAT FLOUR, CONTAINS LESS THAN 2% OF: SALT, CREAM (MILK), SOY PROTEIN CONCENTRATE, YEAST EXTRACT, DEHYDRATED WHEY, FLAVORING, DEHYDRATED GARLIC.

Sounds like a lot of work when you can buy it already canned.

They CAN be canned. Soup manufacturers do it all the time. Read better advice.

The reason is that they do not last as long as "normal" canned foods (noodles are coated to preserve them). The starches in the noodles, potatoes, rice, etc, will dissolve more quickly, as canning will basically overcook the noodles and other starches. I may not be phrasing it properly, but that is what happens, and I learned that by actually having to deal with it when canning chicken noodle soup. The noodles did not last long, perhaps a month, or were very squishy when I reheated them.

it just means dont can them for a long period of time...

They sell noodle soups and canned pasta at any supermarket. Maybe the recipe publishers don't want to be liable in case something goes wrong.

I don’t care