The turning of pages is not necessarily related to the flexibility of pages. Pages man easily even though the page is brittle or stiff.
Sure, watch that video of the brittle, stiff Archimedes Palimpsest (thanks!) pages turning.
Four pages are turned here.
Then compare with the flexible, youthful Sinaiticus pages turning easy-peasy.
Fresh, like a new magazine.
The contrast tells the tale.
It is amazing that people who might be otherwise sharp want to hold on so desperately to the 4th-century myth.