Full ZIP codes are actually 11 digits: a 5 digit prefix, a 4 digit delivery-route-location code, and a 2 digit delivery point number. This 11 digit number uniquely identifies every single place the USPS can deliver mail.
Plus it's not cheap to implement a proper address coding system that conforms to USPS let alone the rest of the world. The USPS data alone is around $4k per year to license (it gets updated every couple months.
Each city will typically have many block extensions, and probably multiple prefixes associated to it.