I might have a possible answer. My mom, like Marie, was a clean freak (not like Marie otherwise thankfully) and we never were allowed to enter thru the front door. If company came and rang the front doorbell that was different. Anybody else, it's the only the back (or side door). It would make sense that especially with food (and the possibility of spilling) they'd go thru the back.

Another "Marie" thing I can relate to? Although not in recent years but in childhood years my mom would leave the plastic on the couch in the living room (that room was like the highlight of the house I guess) Yea we razzed her a lot, God bless her. In later years, she stopped doing that but even til the end, the living was the room you don't mess around in. You just sit.

TIS