Every country has its traditions. It just so happens that there's amateur wrestling in the US so fighters from the US tend to have a strong wrestling base. There's vale tudo and BJJ in brazil, there's kickboxing in central Europe, there's boxing in the UK, there's greco in Eastern Europe, sambo in Russia yada-yada-yada.
Rookie Hammer Squad 2015
Frankie Edgar - Dominick Cruz - Jorge Masvidal - Cat Zingano - Holly Holm