From an Aussie viewpoint there seem to be 2 causes...

1) voting is not compulsory - even though we have "the donkey vote" - being fined for being too lazy to go to the polling booth seems to have some effect - you can always choose to vote 'informal'.

2) The rigid 2 party system (with its formalised selection system) seems to have produced 2 almost indistinguishable flavours of the same political party. 'Minor parties' & 'Independents' are a real force in other cultures - this lack seems to have produced a very narrow minded (and perhaps it could be called 'uneducated') view of the world in the USA.

Robin