What is the reason that Vatican City has a small population?

Answer 1

There is little room for housing in the Vatican. Most of the area is taken up by existing buildings and the Papal Gardens. People cannot simply decide to move to Vatican City. They must be employed there and request housing when it is available.

Answer 2

It's called Vatican "city" because it is inside of a city (it's just that big!) which is the capital of Italy, Rome

Answer 3

The area of Vatican City is only 0.17 square mile, the smallest area of any country in the world.
Because no other country is smaller than it.