Er... what?
OK, maybe this is a Hyperborea*-specific thing. Where I grew up, vanilla was your basic standard ice-cream flavour, what you got if you asked for ice-cream and did not specify; likewise, if you asked for crisps - the things USAns call chips, but what we call chips USAns call fries - without specifying what flavour, the default is ready-salted. Hence a mildly silly family like mine would swap the two around.
There is an unhelpful failure mode here where someone is asked what sort of sugar they want and says "vanilla", meaning normal plain sugar (as opposed to, say, icing sugar) and goes to the cupboard and finds the jar of sugar with the vanilla pods in which is actively vanilla-flavoured sugar and not necessarily the same thing.
The bit about "chocolate and strawberry
and vanilla" in
Good Omens is an accurate represetation of Hyperborean life as of a couple of decades ago.
*Yes, if you want a name covering both Britain and Ireland with no political subtext whatsoever, you have to go back as far as Strabo.