This method is only normal in the USA, most world airports have a sterile area known as "airside" beyond customs and security, so you can buy without needing the gate delivery. US airports were not originally built to accommodate international and domestic flyers as separate, so the customs bonded goods need to be delivered to the gate.

Likewise, in many countries you can now buy your duty free on arrival and this completely avoids all the security, liquid and transit problems.