As a practicable matter... Try pulling some romex through conduit -
especially through a bend in conduit. Not easy to say the least.

Maybe because it is so hard to pull, someone could pull too hard and the
wire would get damaged/break. Or in a bend one side would have too much
tension on it since the jacket tends to hold the whole works together.

Loose individual wires will "slide against each other" at a bend in
conduit.