There’s history around the reason why. It predates the middle finger salute by all accounts and is the OG of feck off salutes tbh.
A commonly repeated legend claims that the two-fingered salute or V sign derives from a gesture made by
longbowmen fighting in the English army at the
Battle of Agincourt (1415) during the
Hundred Years' War, but no written historical
primary sources support this contention.
[27] This origin legend states that English archers believed that those who were captured by the French had their
index and
middle fingers cut off so that they could no longer operate their longbows, and that the V sign was used by uncaptured and victorious archers in a display of defiance against the French.