Marketability in mma is a combination of fighting ability/personality and looks, by looks you don't necessary have to be good looking although it helps but you just have to have a certain look that appeals. Look at these guys for example they all have a memorable look to them that keeps viewers/fans interested in them. Would people really care about machida if he wasn't half japanase and looked like barao? or if Carano looked like shayna blaszler? No one cares about guys that look like your everyday cage fighter like matt brown for example. Notable mentions Bendo, Koscheck, Overeem.