You generally expect the size of an organization to scale with the scope of its activities, especially if its activities include "healthcare" and "building roads."
"Scope of activities", maybe, but there's no inherent reason that has to be equal the rate of growth in the population. You'd hope that government becomes more efficient over time.
Private organizations have profit constraints, and they're constantly striving to become more efficient, cut what doesn't work, and so on. Government has no such constraint.
