Mainly because the U.S. of A still, for the time being, believes in individualism, self reliance and CAPITALISM! Unlike most socialist countries in the E.U., we do not depend on the State to provide and do everything for us.
In the criminal justice system, if you can afford to pay for an attorney, you must. If you can afford to pay your bail, you must. If a bail agent bails you out and you fta, the bail agent IS responsible to bring you back!
Besides I think most other countries look at the U.S.A as still a barbaric country with everyone running around with guns robbing, raping and killing. Partly true. So, I don't think many other countries will follow suit and adopt the Amercian CJS.
In fact, there a good chance that the U.S.of A. will follow other countries and do away with commercial bail and therefore "bounty hunters."