They care because if I expand to the foreign market rather than in the US market because I can bribe my way to advantages, that's competing on very unfair terms

They care because if I expand to the foreign market rather than in the US market because I can bribe my way to advantages, that's competing on very unfair terms with competitors that stay in the US. That and the fact that OECD has a convention against bribery, so if you want to trade in the largest trading block in the world on good terms, you better help enforce the rules.