MMA in it's modern carnation is essentially an American sport, with it's rules tailored towards already existing sports in which Americans excel in (wrestling). Ontop of that the UFC is an American organisation, of course most of the fighters are American.
Many are Brazilian. Of the 8 men's divisions 3 are pure strikers really. Bones and Bendo are American but get many of their wins in striking matches. Cain is a wrestler, but just beat up JDS on the feet. GSP is Canadian and learned wrestling late.....yet he is probably the best wrestler and uses it the most of any champ to secure wins. It is called being well-rounded...not a wrestler.
I agree Wrestling is very important, but then why are so many Brazilians some of the best? Wrestling is defiantly not a big sport there. So why are the so successful?
Pride was a Japanese promotion. So if the UFC is built around American fighters doing American wrestling because it is an American promotion....then tell me why did Brazil and US dominate Pride??? Sure there were more Asian fighters there, but many were sideshows from Pro Wrestling, many were guys who they fed to the Wandys of the organization. So tell me why Japanese fighters didn't dominate the Japanese promotion?