As people have already elaborated on the point, i don't have to repeat that, this situation is uniform to all boxers of all nationalities. They enjoy fighting at home as they benfit from the support of their fanbase directly, they find it easier to promote the fight, they may be in a familiar venue, their confidence is elevated by the implementation of familiar officials or pre fight processes etc. etc.

However i want to turn the mirror on this situation. Why is it that the American boxing public are entitled to accuse English/German/Austrailian/Scandinavian/Russian/Columbian/Mexican fighters of being afraid of fighting outside of their own country? How many Americans regularly travel outside of their respective comfort zone to the back yard of other fighters?
Jeff Lacy did it, Glenn Johnsonn is famous for doing it but how many others?

Two excuses can be used for this refusal to travel.
1)America is the country in which most money can be generated.
2)The fighters fear unfair refereeing/decisions.

Well i believe the solution to these is one and the same. How come other countries can't generate the same money for boxing? Because they are not exposed enough to boxing and the do not have enough big fights to attract capital.
Why is there the potential for unfair decisions? Because there is not enough focus on non-American fights, they are not in the limelight and feel they can get away behind the backs of the larger boxing community.

So the solution: More big fights. Should american big name fighters travel to other boxing nations regularly, undoubtedly it would generate interest. People would begin to anticipate the next big fight, save up so they can go and boxing's popularity would soar due to improved quality of fights, the significance and the respective nations pride at hosting an event such as a world title superfight.
In turn this would remedy the decision/referee problem. With the country and its officials in constant limelight, standards would be improved, wrong decisions and actions would be punishable and avoided.

In summation what is needed to aid boxing globally, to improve the injustices happening in various boxing nations and to stop us all bickering are a few pioneers willing to go and fight. What if Pavlik/Abraham took place in Germany, we'd all watch. HBO wouldn't let anything crooked happen if they adopt Kelly.
If Taylor/Lee were to happen in Ireland. Everybody would watch and a huge crowd would go to see it. If Barerra fought Pac in the Phillipinnes imagine the capital it would raise!

The long and short of it is, everybody is guilty of fighting where they are comfortable if posible and to solve it the big fighters need to lead by example n travel.