Using heat is common in a similar hobby(?), translating (older) Japanese manga. You would use a hair dryer or clothesiron to melt the glue in the spine, pull apart the pages/clean off the glue, and scan them in. That way you don't shave off 2-page spreads. (After scanning, you'd have to clean up the image a lot still, but oh well.) I can imagine here you also just don't want to damage the pages, even if the damage seems infinitesimal.

It doesn't happen so much anymore for manga since things are mostly digital. Though some publishers still publish at 1200x800 (looking at you, Hakusensha!) or worse (I think one site uses like, 900x600?). Mostly these days this would only happen for self-published works (which are still distributed in limited quantities and in physical format only, oftentimes). Or apparently publishers occasionally just...lose the digital files. (Though I can't find where I read this anymore.)