It could be to do with something called “ablaut reduplication”. Very basically English has a - kind of - untaught sound order that native speakers inherently apply to the language. Wikipedia will have an article to explain it better. Specifically the vowel order I-A-O. A great example is the phrase “Bish bash bosh” which is getting coverage recently. (One notable exception is “shit, shower, shave” but that is probably down to the chronology of the actions.)

Go further. For example, people say 'gypped' without knowing it's a pejorative reference to the word 'Gypsy' which is itself a pejorative of the Romani.

Apparently "W" was originally written as "uu" as early as ~600AD, hence the name, however it still used Latin/Roman letters which hadn't yet distinguished between u and v as letters. For at least 700 years, u and v appear to have been considered the same and interchangeable (so "Double U " could look like "uu" or "vv") but it depends on your language whether it was verbally called a "U" or a "V" until the first recorded distinction between the two in a Gothic era alphabet written in 1386. The two apparently did still see some overlap in use until about the 1700s with the turning point appearing to be when the distinction between their capital forms was accepted by the French Academy in 1726.

tl;dr: "Double U" predates the distinction between "U" and "V" so it's up to chance which letter a language called it before it stuck.

Right as incorrect.

Stupid english