https://www.motherjones.com/kevin-drum/2020/02/where-should-...
I suppose we can put them onto military bases.
Edit: Oh, you said city scale. Well, I’ll leave this up anyway.
Because decision making here is less centralized. People have rights, and they will agitate about them. It's not clear where the governmental authority to quarantine an entire city would come from in say, the US. It might be constitutionally challenged, people would get mad and sue. None of that happens in China.
Enforcing quarantine in New York would be very difficult, not least because it's in the middle of a continuous urban agglomeration between DC and Boston with no hard boundaries.
You now have a quarantine zone separating New York City, Long Island, and some of the nearby cities in New York from the rest of the country. The Hudson River provides a pretty decent barrier to travel along the NEC. The Delaware, Potomac, and Susquehanna also provides some barriers, but enforcing quarantine barriers to inland travel is much more difficult (unless you're cutting off the Delmarva entirely).