When I was a kid, I thought vanilla was the flavor for certain things before the real flavor is added (vanilla = no flavor). Obviously that’s not true, but it raises the question of why vanilla is the “default” flavor. Even outside of culinary concerns, “vanilla” connotes something that’s standard, without imagination. Why is that?
I’m sure it’s just because vanilla is the most common ice cream flavour.
Most common = default choice = unconfigured
And because the misconception you had about vanilla meaning unflavoured, is a common one.
My first thought was ice cream and:
*Vanilla is the most popular flavor of ice cream, so lots of people must like it. “Plain vanilla,” however, is something that is basic, standard, and perhaps also drab and dull.
As late as 1946 (see below), “she’s plain vanilla” was a man’s remark that a woman was pure and wholesome. By the 1950s (perhaps the time when half gallons of vanilla ice cream became common in everyone’s freezer), “plain vanilla”—or just “vanilla”—meant something basic and standard. By 1960, “plain vanilla” cars were cars with just the basics and no extras. By the 1980s, this “vanilla” meaning of “just the basics, no extras” was used to describe computers and computer programs. *
from here.
Isn’t vanilla an ingredient often found in other flavors of ice cream, like chocolate?
Anyway, vanilla (as found in ice cream, baked goods, etc.) is a mild, unobtrusive flavor that plays well with others. So vanilla ice cream is often the base to which syrups, toppings, mix-ins, soda, or other flavorings are added (to make sundaes, floats, etc.). If those things aren’t added, you get something plain and relatively uninteresting.
There’s also the factor that artificial vanilla flavor was one of the first flavors to be synthesized and is cheap to make.
In fruit juices, I’d say pear is the vanilla. It will be present in the ingredients of many types of juices because it is so inoffensive and makes a nice filler to cut the price.
There’s also the color issue: vanilla ice cream is white, and white in our culture has connotations of purity as well as associations with blank paper.