Thomas Shey
Legend
This is my experience too, although that's partially because since you can't buy alcohol at self checkout in California they have to have at least one cashier around. When I lived in Kentucky it was pretty normal for stores to only leave the self check outs open past 10 PM or so.
That's why I suspect part of it may be when I come in; if they only schedule one checker for those periods (with probably someone else who can pinch hit if the lines get too busy) they're just not going to tie up someone with the small-number line that many people visiting won't be able to use (though I've also seen managers temporarily manning that just wave people in, but that always seems to destroy the point in having it open).