It's not about guaranteeing at least one day off every week. It's guaranteeing at least one *weekend* day off, which is more challenging to do if the store is open all weekend. As someone whose job can create really weird schedules, not having a day off on the weekend blows. What good does having a day off on Tuesday do? Nothing's happening on a Tuesday.
When I worked at the newspaper in Rochester around 1990, they had the weirdest publication schedule. First, it was an afternoon paper - who does that nowadays? Second, they didn‘t put out a Sunday paper - Saturday afternoon was their big weekend edition. For a lot of my time there, that worked out pretty neat … I’d have Saturday/Sunday off one week, then Sunday/Monday the next. Yes, I guess that meant a three-day weekend every other week, with a one-day weekend the other.
After that I joined the FAA and worked air traffic control, which has to be up and running 7 days a week (at least my facility wasn’t open between 11:30 pm and 5:00 am, so it wasn’t 24/7). That schedule had days off that moved back every four weeks - you’d have Friday/Saturday off for four weeks, then Thursday/Friday for four, then Wednesday/Thursday, etc. We eventually changed that to a six-week rotation, which actually worked pretty well. Every six weeks when your days off changed you had a four-day week (except when you went from Sunday/Monday to Saturday/Sunday, then you’d work five, get Sunday off, then work another five before your weekend).
Some people tended to complain about this schedule saying it was impossible to plan things (having apparently never discovered the concept of a ”calendar”). Towards the end of my career we changed the system so people bid on their days off by seniority, so the most senior controllers got days off around the weekend all year and the least Senior ended up with Wednesday/Thursday all year (and therefore had to work every Friday and Saturday night).