I feel that this is the likely reason. There might have been a common sort of bug or mold or other slow-acting form of infestation which they routinely got rid of by “resetting” the building by burning and rebuilding.
It is believed to ward off evil spirits. Is some sense, it is true, as the smoke has antiseptic and repellant properties - especially from plants such as woodworm.
Stands to reason that any culture which smokes food to preserve it might try fumigating with it
If a fungus sets into wood, and smoke treatment is done after the fact, the smoke won’t be able to penetrate deep enough to completely eradicate something that’s well established.
Also I doubt antifungal properties are needed if temperatures in use can hit 60-80+ C. The spores might survive but even in weekly cycle there is unlikely to be persistent growth that survive.
Unless the birthrates were higher. If people gave birth to litters of fifty of which all but a few were expected to die, the average lifespan would be in the single digits.
I suspect it was exceptional if a woman bore more than 6 children, although obviously some women would have more than ten. I believe the baby boomer generation had large families due to excellent modern medical care post WW2.
Longer average contemporary lifespan in the west has a lot to do with infant/child mortality.