Why is the Google Maps Places Autocomplete API so uncommon in signup forms, but so common in search?

When looking at signup forms, the standard is always to break it down in address, house number, city, zip code, country; all in separate input fields for the user. But when you look at search on Airbnb, Maps, Uber etc. it is so common to use the Google Maps Places Autocomplete API...

Why is it that signup forms do not utilize the same API & ask the user for only one input instead of 5+ separate input fields? Especially on mobile it provides an easier interaction in my opinion.

What are the downsides of the autocomplete single field address that I'm missing?