I agree - the only "public charging stations" I see on any kind of regular basis are EV charging stations. It's been a couple of decades since I remember seeing a USB one, not that I doubt their existence.
They're ubiquitous at conferences and in many trains, planes, airports, hotels, etc. Maybe you mean something different by public but USB charging stations that you don't control are very common especially in the context of places travelers are in. They're probably pretty common in schools, libraries, conference rooms, etc. as well.
