A well vented roof might have kept the odor above where it would be noticed. All houses have sewer vents through the roof. You don’t smell the sewer as you walk down the street.
“The lack of airflow and the fact that the attic wasn’t vented”
“All houses have sewer vents through the roof.”
Those don’t open into the attic. They go straight into the plumbing. And they aren’t to stop sewer smell on the street. They are to keep your drains from vapor-lock.