Why fighters like Bute , Klitschkos or Calzaghe need to go in the hostile US to fight American fighters?

We have all the best fighters. Look at Hatton as soon as he fought a real Champion for the US he got knocked out. In the UK he looked GREAT!!! Not over here. Same thing with Naz and Khan. I wish Joe Calzage would of fought B-hop and Roy Jr when they were on top.