What was the fascination with gelatin and canned food in the 50s-ish era?

I found this recently and I am mildly obsessed.

What I don’t understand is how commonplace it was to shove a bunch of crap into a mound of gelatin. There was one recipe where she ruined a perfectly good potato salad by pouring gelatin into it and molding it. Granted, the blogger and her husband really liked it, but still. Especially when it comes to mayonnaise and gelatin, tuna and gelatin, etc.

Why was everything in a Jell-O mold? And why is it that the recipes are always full of canned foods, like fruit and spaghetti?