What else would you expect? Typing my zip is way easier than going through a list of zipcodes in a dropdown, many of which will be off by one digit in different spots. (ETA: I reread your comment and see what you are expecting)
I like the experience of autocomplete while I'm typing out my street address.
>I have a pet peeve for having to enter my zip code AFTER I've already had to type in the city and state.
The city and state can be derived from the zipcode - so why not simply ask for the zipcode to be typed and then auto-populate the associated city and state.
A few comments here suggest this isn't true.
If you want to reduce input to one field, the autocomplete based on the street address that I brought up is the best experience I've come across.
The problem I've anecdotally seen with autocomplete is there's another property with the same street address as mine but in a different city and different zip code (granted only last digit is different IIRC) about ~15 miles away and on more than one occasion it's caused a few mix-ups.
False. Some ZIP codes even cover multiple States.
I was frustrated that this seemingly open data wasn't openly available. Anything that asks for city+state+zipcode can ask for zip code first, auto populate the rest. For the edge cases where the city is wrong, the person can still type in the city like they would have needed to anyway.
It is worth noting that a package would never get delivered to the wrong place because the city wasn't correct but the ZIP code was. The USPS routes based on ZIP codes, not city/state.