Great question! The reason there is stone behind them more for gaming reasons than historical accuracy. It was designed that way so that the tiles are reversible for use in building dungeons for Clorehaven.
Speaking of Clorehaven, the reason they use a lot of stone in the construction of their buildings is to help shore up their defences from the Goblin Grotto nearby. Being the target of constant raids their buildings have been upgraded.
You do raise an excellent point and one we’re keen to remedy with more traditional wattle and daub (like you can see in the Shadowfey Ruins) when we revise these ranges.
One idea to remedy this would be to paint the internal bricks as mud bricks. Not traditional, but would be easier to explain on some of the poorer sectors of the town.