My initial thought on why americans don't like WRC is because we (as an aggregate) are exclusionists and don't like foreigners winning in any of our events. The most popular sports in the world have players from the global community and we pretty much ignore them. Soccer, F1, WRC, Cricket - HUGE sports. nobody in america likes them. But get a field of players that is basically north american and we'll watch the crap out of it. Baseball, football, nascar, NHRA, basketball. So, I think WRC isn't big in the US because Americans as a whole are jingoists.
Those who control the present control the past, those who control the past, control the future. - George Orwell, 1984.