What's the point? I mean, why blow on one of those things all match long? I go to American football games and make a lot of noise, but only when the opposing offense is lined up to try to get them offside. Otherwise the stadium is silent. What is the point of constant noise during the entire game?
I don't think anyone does, it's just the additive effect of 30,000 people blowing them at random intervals is a constant buzz (particularly on TV, when there's no direction to the audio).
I expect that this is akin to wondering why anyone would want to go to a concert and lay on their camera's flash for two hours to create that annoying "continuous strobe" effect. :)
My theory: World Cup tickets are too expensive for most soccer fans in South Africa, so they are bought by more affluent types, who are not familiar with fan traditions (many don't even know much about soccer), and therefore just blow the vuvuzelas continuously and randomly during the match, because they think that it's the cool thing to do.
"The atmosphere I like and am used to is drowned out by the atmosphere you like and are used to."
Yes, it's an endless drone on TV and my wife doesn't love it, but it is unique to this World Cup and gives it its own flavour. Come visit me in Summer and our heat is dry and merciless all day. Visit the tropics and the night is filled with cicadas for hours on end. They're things which not everyone will love, but they help define these places.
The vuvuzelas are not forever, but they help define the 2010 WC.