The primary function of houses is to increase the population limit. However, various other structures do that too, thus functionally overlapping with the house. For civic centres, it's necessary they increase the population limit, to allow rebuilding after one has lost their houses and units. For other structures (dock, fortess, temple, etc.) it's rather unnecessary, those structures already have a clear function and don't really need to increase the population limit, therefore it's removed from those.