I'm sure the change happened at different times in different places. But in the the late 70s, even in a big city like Boston/Cambridge, almost nothing was open on Sunday. If you played sports or had other activities on a Saturday, you basically had to find a way to carve half a day out of classes etc. to run errands.

And to one of the parent's points, when the debate about Sunday store closing laws came up in Louisiana in the 80s, one of the arguments against making changes was that mom and pop stores, largely staffed by the owners, couldn't realistically open for seven days while, for the big chains, it was just a dollars and cents calculation.

implicit assumption that having things closed one day a week is bad.

It is perhaps less convenient, but that doesn't make it bad. Lived in an EU country until recently, where everything is closed on Sunday. It makes that day much more restful, and it doesn't take long to learn to get your shopping done on Saturday.

Also, it is still illegal to use power tools outside on Sunday. Which means you aren't disturbed by your neighbor's leaf blower.

Honestly, I prefer 1 day a week of true rest over more convenience but never a true rest.