Fiber optic strands are glass rods (solid interior) instead of tubes (hollow cylinder). The two shapes have different strength properties per unit mass [1, 2].

[1] https://physics.stackexchange.com/questions/12913/hollow-tub...

[2] https://www.mtbiker.sk/forum/download/file.php?id=207637

Traditionally, yes.

Hollow air core fibre does exist and seems to be touted as the next big thing though.

https://www.optcore.net/hollow-core-fiber-introduction/#h-wh...

Current implementations break from simple vibrations such as a bus driving down the road and shaking the ducts the fibre is in. Lots of work required still. Crazy expensive and crazy fragile.

Pretty much every solid material gets vastly more bendable when it's very thin.

(From vague memory, stiffness is proportional to the cube of the thickness.)