It's very effective naming strategy. It's called VanJS not Vanilla JavaScript. But it's kinda hard to remember Van, or any letters really. By association of it's main quality which is small size/simplicity with common term such as vanilla JavaScript, suddenly VanJS becomes memorable.

Similarly vanilla js was named like that, after common term describing plain flavor of icecream. Which was weird to me, and I learned that as a non-native speaker only after I heard about vanilla js.