The problem is rarely the whole document
A batch fed through a scanner the wrong way round leaves a handful of pages on their side and the rest perfectly fine. Rotating everything fixes those and breaks the others.
So the tedious part is not the rotating, it is picking out which pages need it — and every rotate tool leaves you to do that by eye, clicking through thumbnails one at a time.
“Only sideways” selects every landscape page in one press. The detection accounts for rotation already stored on the page, so a portrait page that was previously turned 90° is correctly identified as currently landscape.