"For my friends everything, for my enemies the law" - Óscar R. Benavides

Trade agreements limit the size of import tariffs that can be imposed and this bypasses those limits nicely. (Not that ZTE weren't stupid to do this in the first place).

On the other hand if it suits the right company they can do what they want. For example massive amounts of vanadium were shipped from the Congo to the US during sanctions for use by the US aircraft industry.