I'm not sure on this, but I think it works in reverse of what you expect. You expect that you will need to build huts to increase the population, but I think they build huts 'because of' an increase in population.

In other words, I think there's a set population level that triggers the builder's "urge" to build a hut.

Sort of the opposite of that saying "If you build it, they will come". In VS, it's "if they come, they will build".