I think it's been said here before, but
Jell-O salads were historically lemon, until they added lime as a flavor. Tastes and budgets were such that people accepted lemon or lime Jell-O salads as a way of using up leftovers and stretching savory ingredients. Then in the 1960s Jell-O sold savory flavors specifically for use in salads/aspics, noting in the marketing that it's more appropriate to use a non-sweet base for a savory salad.
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This is a job for a forensic culinary anthropologist, but Aunt Myrna's recipe could have originated as a fully savory one, maybe even from a Jell-O sponsored feature in a ladies' magazine, then been elaborated on and changed as savory Jell-O was discontinued, as other recipes were remembered, as different leftovers were available in the kitchen. Other than chemical considerations like pineapple, the historical draw of a Jell-O salad was that you can put
anything in there.